The ones I'm currently interested in playing:

Barbarians of Lemuria/Honor + Intrigue
Openquest (or Clockwork & Chivalry with the new Clockwork & Cthulhu book)
Mongoose Traveller with Cthonian Stars
Conspiracy X 2.0
Supers!
Heart & Souls
League of Adventures/All For One
Servants of Gaius
Qin
Lamentations of the Flame Princess

I'm always readily play a superhero game. I've been on a supers trip for a few years now - I say I'm making up for lost time when my group wasn't open to supers. I'm not too fussed about the system as long as it's not too slow, complicated or jarring.

I'd like to play either Shadowrun or Deadlands. I've only ever manage to play the odd session here and there of either game, I feel there is unfinished business. To be honest I'd be happy with regular Western or anything with a bit of cyberpunk vibe too.

Also, I'd love to play in a bona-fida Ghostbusters campaign. Not slapstick one-shot, but an actually campaign with connected adventures, recurrent foes and an overall story arc. And proton packs.

Hmmm, surprisingly tough question.

TSR-era D&D. We played a two-year-long Castles & Crusades game, which is close enough, I guess... but our sessions were too few and far between, and the campaign ended not with a bang but with a whimper, and our group of miscreants & malcontents actually fled when the DM offered us a hook into the endgame (by having the city elders offer us lordship of our besieged home base). So I can safely say my thirst for old-school goodness wasn't properly sated.

A hard SF game. We had a regular GURPS Space game back in the day, with strong space-operatic sensibilities (more accurately, it was a B5 rip-off), and it was fun, but I wish we could play a game in which the hazards of space travel and planetary exploration were played up, and players were encouraged to come up with interesting solutions.

FATE. It didn't click for me as a GM (sorry, "Story Teller"), but my players loved it, and I'd like to try it from a player's seat.

A storygame. I'm not sure I'd like it but I want to see what the fuss is all about. I'm not sure which, but Apocalypse World does look snazzy (except for "sex moves". I'd rather ignore that part). Maybe Octane. Or good ol' Sorcerer. I'd just steer clear of the stupid shit like Poison'd or Hell For Leather, or misery tourism like Grey Ranks, or super artsy fartsy stuff like Polaris.

Classic campaigns. Masks of Nyarlathotep, for CoC; The Enemy Within, for WFRP 1e; and the Slavers-Giants-Drow proto-adventure-path, for AD&D 1e.