I've tried to put together a list of interesting and useful powers, but naturally not every one of them will fit every game. Feel free to fold, spindle, mutilate, cannibalize, or genetically modify this table and the descriptions of power to suit your own needs and tastes.
How many powers should a weapon have? I'd say 1 to 4, depending on how powerful you want it to be, but of course that's a completely non-binding suggestion. Duplicates may either be re-rolled or increase the power or intensity of the effect, as desired.
03-04 Animal Totem
05-06 Armor Destroying
07-12 Attack Bonus, +1
13-15 Attack Bonus, +2
16 Attack Bonus, +3
31-36 Damage Bonus, +1
37-39 Damage Bonus, +2
40 Damage Bonus, +3
41-43 Detect Enemies
44-45 Detect Evil
46-47 Detect Gems
48-49 Detect Magic
50-52 Detect Metal
53-54 Detect Water
55 Dimensional Rift
71-72 Light, Moonlight
73-74 Light, Starlight
75-76 Light, Sunlight
95-96 Vampiric strike
Absorbing: When the weapon is used to strike the killing blow against a creature with a special attack, it absorbs that mode of attack, i.e. fire from a red dragon, petrification from a medusa, or poison from a cobra. If the special attack causes points of damage, the Absorbing weapon will deal an additional 1d6 points of damage from that attack form. Otherwise, the effect is exactly as that of the monster, including saving throws allowed, inflicted on a successful attack. Whenever a new creature is slain with the weapon, the previous attack form is lost and the new one, if any, is gained. Slaying a foe with no special attack "empties" the weapon until another creature with a special attack is killed.
Animal Totem: The weapon grants the user influence over a class of animals; for example, bears, felines, canines, or birds. Both normal and giant varieties are affected. Animals of that type will not attack the wielder while he or she holds the weapon unless charmed or similarly controlled. Additionally, once per day the wielder may summon animals of the appropriate type if any are within 360' (360 yards outdoors.) The weapon summons 2 Hit Dice of animals per level of the wielder (minimum of one creature) which serve in any way they are able for 1 turn.
Armor Destroying: On a successful attack, the weapon reduces the AC of the target's armor or shield by 1 point. This may be due to rending, crushing, corrosion, or any other sort of damage that seems appropriate. Only armor worn is affected; armor that is part of a creature's body, or that is entirely magical (e.g. rings of protection) is not affected. If the armor's benefit is entirely destroyed, the armor is ruined; otherwise, it may be repaired by a competent smith.
Attack Bonus: The weapon confers the given bonus to the wielder's attack rolls.
Bane: A bane weapon is specially enchanted against a specific type of opponent, such as dragons, lycanthropes, undead, constructs, elementals, etc. Banes come in three strengths (roll 1d6). Minor (1-3): Increases the damage die of the weapon by one size against the given opponents. Lesser (4-5): Increases the damage die by one size, roll twice and take higher. Greater (6): Increase the damage die, roll twice and apply total.
Charming: Once per day the weapon may be used to cast a charm effect. Roll 1d6: 1-3 Charm Person; 4-5 Charm Monster; 6 Charm Plant.
Concealment: When not in use, the weapon may be transformed into an innocuous article of jewelry on the wielder's weapon hand or arm. Small weapons such as daggers become rings, while larger ones become bracelets or bracers. Any non-attack powers of the weapon remain active and usable in concealed form.
Courage: When the weapon is held aloft, it radiates an aura of courage in a 10' radius. All allies within the area of effect are immune to fear effects and need not check morale, if applicable.
Crushing/Slicing: On a natural attack roll of 19 or 20, the target must save vs. death ray or be instantly reduced to 0 hit points.
Damage Bonus: The weapon increases the damage inflicted on a successful hit by the amount given. Choose or roll 1d6 to determine the source of the bonus.
1 Acid: On command, the weapon drips with corrosive acid.
2 Fire: Flames dance along the weapon's edge or striking surface, and may be used to ignite flammable materials
3 Force: The weapon imparts extra impact to each swing.
4 Frost: The blade or striking head of the weapon is constantly glazed with frost, and may be used to freeze small volumes of water or extinguish flames.
5: Keen edge: The weapon is especially sharp. (Treat as Force for blunt weapons.)
6: Lightning: Electric sparks dance along the weapon's surface; +1 to hit metal armored opponents.
Detect Enemies: When unsheathed and held, the weapon alerts its user to the presence of a particular type of creatures, such as humanoids, dragons, undead, etc. within 120'. It may do so by glowing, vibrating, or chiming softly.
Detect Evil: Similar to Detect Enemies, but alerts the user to evil intentions or enchantments within 30'.
Detect Gems: The weapon can sense the presence of gemstones, either cut or uncut, within 60', and will subtly pull toward the richest cache.
Detect Magic: The weapon can sense the presence of magical effects within 20'. The exact source cannot be determined, only the presence and the general direction.
Detect Metal: The weapon can sense the presence of metals within 60', and will subtly pull toward the largest mass.
Detect Water: The weapon can sense the presence of fresh water within 360', and subtly pulls toward the largest quantity.
Dimensional Rift: Once per day, the weapon may be used to cut or smash a hole in the fabric of reality. The user and up to one other creature may pass through it to another location, as either a Dimension Door or Teleport spell. The rift remains open for 1 round.
Fear: The weapon radiates an aura of fear in a 30' radius. All enemies of the user within the area have their morale penalized by -1. Additionally, an opponent struck must save vs. spells or cower in fear for 1d6 rounds.
Frenzy: Each time the weapon is used to strike a killing blow, it gains +1 to attack and +1 to damage, to a maximum of +5. All bonuses expire when one turn passes in which the weapon is not used to slay a creature.
Healing: Once per day, the weapon user may heal himself or another person or creature. Roll 1d6 for the strength of the healing magic: 1-3: 1d6+1; 4-5: 2d6+2; 6: 3d6+3.
Holy: The weapon is imbued with holy radiance, emitting constant protection from evil and turn undead effects in a 10' radius. The weapon user turns undead as if a cleric of 3rd level. If the user is a cleric of 3rd level or higher, he or she turns undead as if 1 level higher than actual level.
Hypnosis: Opponents are fascinated by the movements of the weapon. By spending one round twirling, swinging, and spinning the weapon, the wielder may mesmerize any creature watching. This includes all creatures in melee with the user, and may include others, at the DM's discretion. Each must make a saving throw vs. paralyzation or be unable to act for the next 1d4 rounds.
Leadership: Potential hirelings, henchmen, and mercenaries react to the weapon's bearer at +1. As long as the weapon bearer is within 60' they also check morale at +1. Even if a morale check is failed, so long as the weapon user is commanding them, the NPCs will retreat in as orderly a fashion as possible. A group of two or more NPCs fighting in formation according to the orders of the weapon user receive a +1 bonus to attack rolls and AC.
Light, Moonlight: The weapon radiates light like the pale silvery light of the full moon in a 15' radius. Lycanthropes within the area of effect must save vs. spells or involuntarily transform to their beast forms.
Light, Starlight: The weapon radiates cold light like that of a starry sky in a 10' radius. Hidden things illuminated by the light, including traps and secret doors, will be revealed on a 1 on 1d6, or with a +1 bonus if the wielder actively searches.
Light, Sunlight: The weapon radiates warm golden light like the sun in a radius of 30'. Creatures which are averse to daylight suffer the same penalties within the weapon's glow.
Nullifying: Enchanted items struck by the weapon are deactivated for 1 turn. This includes both permanent magic items and those affected by a spell. Spell duration resumes in progress, if any time remains. This power has no effect on enchantments on creatures, only on items.
Paralyzing: A target struck by the weapon must save vs. paralysis or be held for 1d6 rounds.
Petrifying: A target struck by the weapon must save vs. petrification or be turned to stone. The wielder of the weapon is aged 5 years.
Phantom: The weapon's blade or striking head is translucent and insubstantial. It is unhindered by non-magical armor and shields, and can strike incorporeal creatures such as shadows and wraiths. Magical armor and natural armor such as a dragon's work normally against Phantom weapons.
Protection: The weapon grants a defensive bonus to the user's Armor Class. Roll 1d8: 1-5 +1; 6-7 +2; 8 +3. The bonus may be used to defend another creature within reach rather than the weapon user.
Purity: Food or water touched by the weapon will be affected as if by a purify food and water spell. Additionally, while the weapon is held, the user is immune to the effects of foul smells such as stinking clouds and the stench of troglodytes.
Reanimating: Humanoids slain by the weapon will rise in 2 rounds as zombies under the control of the weapon user. Up to 2 zombies per level of experience of the user may be controlled at once; any in excess of this number are uncontrolled. They will not attack the weapon user so long as he holds the weapon, but may attack other members of his or her party. They may be turned normally.
Silence: The weapon makes no sound when striking any solid material. Instead, a wave of silence radiates to a 10' range. Each burst of silence lasts 1 round, and the effect may be repeated as often as desired.
Summoning: Once per day, the weapon may summon a creature to assist in any way the user wishes for 1 turn. If the weapon contains a bound spirit, this is the bound creature being released to perform the service. Otherwise, the weapon summons a creature of 6 Hit Dice or fewer, of one of the following types: an angel or demon, a fairy, an elemental being, or a spirit of a dead person or creature. Exact creature type and statistics are left to the DM to determine.
Unholy: The weapon radiates unholy power in a 10' radius. This acts as a protection from evil spell, but against good creatures. Additionally, the user may attempt to control undead by making a turning roll as if a 3rd level cleric. A cleric of 3rd level or higher makes the turning roll at one level higher than his actual level.
Vampiric: The weapon transfers half of the damage caused to creatures struck, rounded down, to its user. The user may not increase his or her hit points beyond the normal maximum, and may not absorb more hp than the target actually has, regardless of the damage roll.
Venom: A creature struck must save vs. poison or suffer 1d6 points of damage per round for 1d6 rounds. Creatures immune to poison are unaffected.
Will: The wielder of the weapon is immune to the effects of mind-affecting magic such as sleep and charm spells as long as the weapon is held.
More tables of weapon features to come, including materials, source of powers, quirks and hindrances to make weapons a little more interesting, and minor powers appropriate for low-level characters and low-magic campaigns!