7th Sea--Played it once. Lots of fun, especially for a pirate-phile like myself.
Star Wars d20--Also played once. Love SW, love the d20 version of it (played the old d6/WEG version a couple of times, but I like the d20 version better for some reason. More crunch, I suppose).
Fading Suns--Love the setting. Both the d20 and the original system version have their own strengths. Dunno which one I would use if I ran it.
Deadlands--Have heard only good things about it, never had a chance to play it.
Castle Falkenstien--Dunno how the whole playing cards-vs-dice thing works, but I like the setting.
Jovian Chronicles--Played the Mekton version of this for a while. I don't know too much about the Shilouette system, but I'd be willing to give it a try.
Heavy Gear--I own about half of the books for this game, yet I have never played or ran it. How pathetic is that? Love the setting, same unfamiliarity issue with the mechanics as with Jovian Chronicles (same system, after all).
Last, but certainly not least (quite the contrary, in fact), is Mekton Zeta/Fuzion. If you use the mecha rules from MKZ and the character rules from Fuzion, you have an awesome game. It's been a long time since I've had the chance to play or run MKZ, but those were some great games.