Well, I'm not a regular poster on this board, but I'll chime in. Other than 1st ed AD&D, my favorite non-oneshot games to run or play are Chaosium's 2nd ed Runequest, Classic Traveller, and Call of Cthulhu. I also bulldozered my way through running a Fading Suns campaign, but I have to say that I'm not really a fan of the system.
Minor games I'll do once in a while would include old TSR Gamma World / Metamorphosis Alpha, Paranoia, Stormbringer, FASA Star Trek, and WEG Star Wars d6.
I still haven't really got to play Warhammer 1st ed or Rogue Trader. And I have yet to find a smooth-running Tekumel system.