Magical weapons ought to be more than just a bundle of powers. Creating an appearance (including materials which comprise it) and determining the nature of its enchantments gives a weapon a lot more character than simply generating powers. You can start from any point you like, rolling or choosing powers, power source, and materials in any order. Sometimes a particular roll may suggest results from the other tables without rolling. Other times, you might wish to roll all the way through and figure out how the results mesh to create a credible and interesting weapon.
Power sources: Roll 1d10:
1 Bound spirit: The essence of some creature is bound within the weapon. The spirit may be fully conscious and communicate with the user, dormant and uncommunicative, or in a sort of limbo or dream-state from which it sends strange subconscious messages. The spirit may be bound willingly or unwillingly, or even unwittingly; perhaps it is completely unaware of its circumstances. Roll 1d6 to determine the type of spirit:
1 Angel or Demon: Extraplanar entities of good or evil disposition. An angelic or demonic weapon may not suffer itself to be wielded by a person of the opposite ethos, or may attempt to influence, control, or seduce such a person into committing acts of good or evil.
2 Deceased soul: The spirit of a dead person. The temperament and disposition of this being may fall anywhere in the range of human or demi-human personality.
3 Elemental: A being from one of the elemental planes, or strongly associated with one of the four elements. May be either a proper elemental or a being such as an efreeti, djinni, undine, or xorn. Elementals tend to be of neutral disposition, either unconcerned with or oblivious to how their powers are employed by the weapon's wielder. Roll 1d4: 1 Air, 2 Water, 3 Earth, 4 Fire.
4 Fairy: A fey spirit such as a sprite, nymph, nixie, sylph, leprechaun, brownie, or similar. Fairies may be benevolent or malicious, but often have a mischievous disposition.
5 Monster: The essence of an intelligent non-human living creature, particularly one with fantastic or magical abilities such as a dragon, harpy, medusa, or troll. The spirit's temperament and interests will correspond to those of the monster type.
6 Split personality: The weapon contains two distinct spirits of the same general type but opposing personalities. (roll again, rerolling further 6s.) The two may be present simultaneously, or else one emerges when the other is submerged (possibly at particular times of day or during particular events.) They may be aware of one another or completely oblivious to the other's existence.
2 Circumstance: The weapon was made or enchanted by particular circumstance not conforming to any other method on this list; e.g. forged under an auspicious celestial alignment, dipped in the River Styx, buried beneath a black obelisk for 100 years.
3 Divine power: The weapon has been blessed with power by a god, goddess, demigod, or other powerful supernatural being. The being may have created the weapon of its own initiative, or blessed it at the behest of a high-level cleric. Divine powers are always crafted to serve the purposes of the deity, which are not necessarily perfectly aligned with those of the cleric or the church.
4 Enchanted: The weapon has been imbued with magical energy by a wizard or sorcerer. These weapons tend to be carefully designed with the needs of the maker or the person for whom it is made in mind.
5 Fairy charm: The weapon was created by fairies or other beings from a realm with different physical laws from the primary campaign world. These enchantments tend to be capricious and unpredictable in the hands of mortals.
6 Heroic weapon: The weapon was wielded by a great hero (or villain) and absorbed some of his or her legendary skill, and perhaps a measure of personality and ethos as well.
7 Runes: The weapon is engraved with runes of power. These may include runes that channel particular magics or energies, such as fire or light, and the runic true names of creatures to be specially affected by the weapon. With a read magic spell, runes may be deciphered to reveal the powers and purpose of the weapon.
8 Special material: The weapon's special properties derive from its material composition, possibly in combination with special techniques for forging or shaping it. The special material may make up the bulk of the weapon, or its edge or striking surface, or even an adornment such as an inlay or jewel.
9 Technology: The weapon is actually an artifact of a
technologically advanced society; though its powers seem to be magic,
they do not detect as magical and cannot be dispelled.
10 Roll again twice, re-rolling any further results of 10.
Material: Roll 1d20
Magical weapons may appear perfectly ordinary or wildly exotic or just plain odd. If desired, roll twice or three times: Once for the blade or striking head, once for the haft or handle, and once for adornments such as inlays and pommels. Materials ordinarily unsuited to weapons, such as gold or glass, or unsuitable for certain weapons (e.g. sword of stone or wood) may be magically durable, or the weapon may just be easily damaged or broken.
3 Silver: Will harm creatures normally vulnerable to silver.
4-5 Common alloy: A metallic alloy of no special properties other than steel; e.g. bronze, brass, pewter.
6 Gold or other precious metal
7 Cold-forged iron: May harm some creatures not vulnerable to ordinary or silver weapons.
8 Fantastic metal: Mithril, adamantium, star-metal, or any metal in your campaign that has mystical properties.
9 Special alloy: A metallic alloy that has special properties in the campaign. For example, dwarven or elven steel.
10 Glass: Any color you like, transparent or opaque.
11 Gemstone: Any precious or semi-precious stone, such as diamond, emerald, ruby, sapphire, opal, jade, topaz, malachite, tourmaline, citrine, pearl (or mother-of-pearl), jasper, coral, etc.
12 Stone: Any non-precious, non-metallic mineral; for example, flint, obsidian, basalt, marble, limestone.
13-14 Bone, animal: From any natural mammal, bird, fish, amphibian, or reptile; includes teeth, tusks, and horns.
15 Bone, human or demihuman
16 Bone, fantastic creature: From creatures such as owlbears, griffons, pegasi, or dragons. Includes teeth, tusks, and horns.
17 Elemental material: Ice that doesn't melt, solid fire or air, elemental earth, or some other pure elemental matter.
18-19 Common wood: Pine, oak, ash, hickory, or any other wood commonly harvested for carpentry or construction.
20 Fantastic wood: Mallorn, treant, the bark of the World Tree, a branch from a dryad's soul-tree, or any other wood that has magical qualities in your campaign.