3.5 elves are both woodsy and civilized, wild and cultured.
Elves are short and slim, pale-skinned with dark hair and green eyes (but no facial hair). Elves "trance" instead of sleep, and they live more than 700 years.
But the 3.5 PHB1 reveals a fundamental problem with elves which just gets worse as the edition continued to talk about them in other books. D&D elves draw on two primary sources: Tolkien and the Child ballads (though it's likely that the Child influence is mostly filtered through a handful of secondary sources). These two notions of elfness conflict, and so D&D elves are peaceful, but warlike. They are close to nature, but highly civilized. They have a broad perspective and rarely experience extreme emotions, but they respond to insults with violence.
This vision of elves is schizophrenic, totally different depending on who's writing them and just plain hard to nail down, so 4e wisely split them into two races. I'll mention the drow as well, for completeness and because their history is tied to the origin of elves.
Please keep in mind, though, that the 4e Points of Light setting is not firmly established. You will find variations and even contradictions in the lore depending on what you read where; they deliberately muck about a bit with continuity, because ultimately such things are in the hands of the GM. What follows is my understanding of the general history, based on trying to piece together disparate conflicting sources.
Eladrin are the Tolkien-like High Elves and drow are their disowned relations.
Civilized and regal and aloof, innately attuned to the arcane arts, eladrin are the flagship race of the Feywild. When the dark goddess Lolth rebelled against the other two Feywild gods, a group of eladrin joined her side in the ensuing war. Lolth lost, and her followers were cast out. They moved into the Underdark and became the dark-skinned, insane, spider-worshipping drow.
Eladrin are slim, often fair, with hair in pale metallic colors, pupil-less eyes in vibrant cool colors, and pointy ears. They have no facial hair and little body hair, and stand about as tall as humans. Eladrin "trance" instead of sleep, and they usually live over 300 years.
The elf is the eladrin's hillbilly cousin.
During and after this war, many eladrin left the Feywild entirely and settled in the Mortal/Material Plane. After generations, they became elves: closer to nature and slightly shorter-lived than their eladrin brethren (though neither race lives nearly so long as the 3.5 elf), they are hunstmen and craftsmen. Elves live in trees instead of spires and are more associated with primal magic than with the arcane arts.
Elves are slender, with tan and brown skin colors. Their hair comes in the colors of the leaves in autumn. Like eladrin, they have pointy ears, no facial hair, cool-colored eyes (though they have pupils), and are about as tall as humans. Elves sleep like humans do, and they usually live at least 200 years.
