Continuing my project to rebuild the race-as-class demihumans of classic D&D to operate on the same framework of level advancement as the human classes, and at the same time distinguish them...I give you the Elf.
The Elf class as written, Moldvay/Cook and Mentzer editions
Hit Dice: d6 (+2 hp at 10th level)
Armor: Any, may use shields
Special abilities: Magic spells, infravision 60' range, immune to ghoul paralysis, find secret doors 2 in 6, bonus languages
Base XP: 4,000
Maximum level: 10
Beyond max level: Attack Ranks allow the elf to improve attack rolls up to the equivalent of Fighter level 25-27. Also high level combat options for fighters, multiple attacks, and half damage from dragon breath.
The Elf is a versatile and formidable character combining most of the abilities of the fighter and magic-user classes. Other than the level limit, the only balancing factor is the high XP requirement for advancement - twice that of the fighter class or 1.6 times that of the magic-user. Because of this, an elf character often lags a level or two behind the other members of an adventuring party. Fighters, dwarves, and even halflings are likely to have a full hit die or more over the party elf, and so are more capable of taking on high-risk opponents in melee. The magic-user is going to get the big bang spells well before the elf (20,000 XP to reach 5th level for the M-U vs. 32,000 for the elf.) On the other hand, the elf's armor and superior hit points make him a little more likely to survive to that level. Sometimes slow and steady really does win the race.
The Elf, revised
Looking at a class that offers the best of both worlds of fighter and magic-user, and a healthy smattering of perks on top of that, the first impulse is to tone it down considerably. I'm a bit reluctant to do that, though, for a couple reasons. One is that in most of the literary and mythic references, elves are held in awe by humans, so my impression is that they're supposed to be powerful. The other is that what I'm after is not absolute parity of power between the classes, but a unique experience and valid reasons for playing each one.
That said, I'm not aware of any source material in which elves can see in total darkness, so infravision could be jettisoned without a drastic reimagining of the Elf archetype. At most, elves are supposed to have sharper vision than humans, and to see better in low light like a moonlit night, not actual dark-vision. The bonus for finding secret doors represents that well enough.
Another way to differentiate the Elf from the Magic-user would be with modified spell lists. The Elves of Alfheim Gazetteer (GAZ5) has such a list. The Tall Tales of the Wee Folk supplement (PC1) has a list of Fairy Charms that would also serve nicely, and the free Companion Expansion from Barrataria Games has a "wildwood elf" class that uses the same spells as its druid class and would work nicely for the B/X elf as well. If none of those lists really feels right, the easiest solution while staying true to the archetype would be to simply delete all spells that cause direct harm to a target creature, either through points of damage (magic missile, fireball, etc.) or otherwise (death spell, cloudkill, power word kill, and so on.) This reserves the "weapon of mass destruction" role almost exclusively to the magic-user class.
Between those tweaks and the class's high XP requirements, I'd consider that done, but if that's not far enough for your taste, use the Cleric/Thief combat tables rather than the Fighter one. Unless you're operating on a very Tolkienesque vision of elf as legendary warrior, blunting its combat progression a little doesn't strain the archetype at all.
Up until 10th level, an elf character is considered to be "finding himself," exploring his affinities for both magic and physical combat. At level 10, the elf must decide which vocation to pursue seriously. Either path uses the same XP table. An elf choosing combat as his or her primary vocation continues to advance on the Fighter combat matrix and gains 2 hp per level. An elf choosing magic continues to advance on the Magic-user spell table, and on the Magic-user combat table once that exceeds the skill of a 10th-level fighter (which occurs at level 21 in the Mentzer Companion attack matrix), and gains 1 hp per level.
Note that the Elf Warrior is still able to cast spells up to the 10th level of ability, and the Elf Wizard is still able to use weapons and wear armor.
The special abilities listed below apply only to Elf Warriors. Use the standard Magic-user spell tables for Elf Wizards.
1,000,000 12 Parry,* Disarm.**
2,200,000 18 Two attacks per round.***
2,800,000 21 Half damage from breath weapons, save for 1/4.
4,600,000 30 Three attacks per round.***
* The Elf Warrior may forego one attack per round in order to block a single incoming attack with a weapon held in hand. The parry requires a successful saving throw vs. Death Ray. On a made save, the attack is deflected and causes no damage. Attacks from creatures larger than an ogre may not be parried in this way.
** A Disarm attempt requires a standard attack roll. If the attack hits, the target must save vs. Paralysis. If the save is missed, the target drops its weapon. Unarmed opponents may not be disarmed. Disarming an opponent wielding a two-handed weapon requires two consecutive successful disarm attempts, i.e. two in the same round or one at the end of a round and another at the beginning of the next round.
(Parry and Disarm are variations on the Fighter Combat Options of the same names from the official Companion Set; if desired, use those mechanics unaltered rather than the ones given here. Elves under these rules do NOT gain the Smash option.)
*** To reflect the perception of Elves as graceful beings, multiple attacks are possible only with a one-handed, non-bludgeoning weapon. Multiple attacks can be applied to long or short bows as well, to simulate the Elf's fabled skill at archery.
I strongly prefer the B/X saving throw progression over the Mentzer/Rules Cyclopedia tables, as it leaves a lot more room for improvement after level 10. For Elf Warriors, use either the 10th level Elf saving throw or the Fighter save for the character's actual level, whichever is better. Elf Wizards use Elf or Magic-user saves, again, whichever is better. (As far as Fighter and Magic-user saving throw tables, I prefer the ones from The B/X Companion over the official tables given in the TSR Companion and Master sets or the Rules Cyclopedia.)