EricNoah said:D&D for me. If someone were willing to run, say, D20 Modern, I would play, but probably not GM as I think I'd have trouble coming up with adventure ideas for a whole campaign. (One-shot gaming, I could probably do that).
And I'm a one-system guy, not out of loyalty but out of laziness. Some people really enjoy learning new rules for new games. Me -- I don't. I find that a chore.