D&D Retroclones:
OSRIC, a retroclone of AD&D1e.
Labyrinth Lord, a retronclone of B/X D&D.
Swords and Wizardry, a retroclone of original (0e) D&D. There is a swords and sorcery variant, Crypts and Things, which is supposed to be quite good.
Dark Dungeons, a retroclone of rules compendium BXCMI...