Spirit of the Century: I purchased this awhile back, went through character creation - fun in of itself - but haven't run or played it yet. I'm hoping to highjack the Hunter game I'm in now in a few weeks and run a session or two of SotC. The Fate system underlying it is easy, aspects is the most interesting game mechanic I've run across, and it just looks so damn fun it's ridiculous.
Monte Cook's World of Darkness: After I realized I was making a lot of harsh judgments against 4e without really playing it, I realized I did the same with McWoD. It's not the WoD I'm used to, but it could still prove to be a good game. Anyone play it? Thoughts?
Roanoke: Another game I've purchased but not played. I'll probably only get a one shot out of it, but the setting is ripe for good horror.
Nobilis: Another how-the-fuck-have-I-owned-this-and-not-played-it!? game. You are the representation of some abstract concept: Fear, unrequited love, conspiracy, and you stand for and against others like you and those things that wish to unmake you.
Burning Wheel: The chaotic and dirty combat system looks unique. Also, after playing mostly in contemporary WoD settings, I'd really like to try more past/fantasy settings.
Dogs in the Vineyard: Mostly want to play it because of its reputation.
And there's at least twenty more books to throw on this list... but I'm feeling lazy.