Over at Rather Gamey, Ark has listed his top seven played and run games. Seems like something to post, so I thought I'd go ahead and do the same. Note that these are not lists of favorite games, but rather the games that have actually been played/run most.
Of games I've played, it seems to me like this:
1) GURPS 3E
3) Call of Cthulhu
5) AD&D 1E
7) Champions (1st-3rd edition HERO System)
Of games I've run, it is most likely in this order:
3) GURPS 3E
4) AD&D 1E
5) Vampire: The Masquerade
6) Top Secret
7) Any number of one-shots. I'll say Space 1889 because it should be on here somewhere.
That is to say, I don't think that I've run any game other than those top 6 more than once. I wish that I'd done so with, say, Space 1889 or CORPS, but not yet.
I really should run a MegaTraveller game sometime. I've got the megadungeon thing up first, though, in order to get back into the swing of running stuff. I've laid some more firm plans toward that today, in fact.