Chaosiums "Basic Roleplaying" system is a game which has fairly coherent, realistic and elegant rules. It comes in several implementations, such as RuneQuest, Call of Cthulhu, Stormbringer, Elric, Elfquest, Ringworld and Nephilim. You'll find here rules, equipment and settings for use with BRP-Rules.
Fantasy
Fantasy-Backgrounds
Space
Science Fiction with RQ Rules
MiddleEarth
Rules for Middle Earth
Houserules
Rules additions, clarifications and errata
Software
Computer software for use with the game.