Shadowrun -- I've always despised magic mixed with tech, but I love this game. I've been told it's my best game to GM. Unfortunately, my current group isn't so hot on tech in any form.
Vampire: The Masquerade -- I've always liked Vampires, so this was an easy sell. I've quipped that the Storyteller system is the worst mechanics that remain playable, but it actually does what it intended fairly well.
Mage: the Ascension -- Like Shadowrun, this game took a concept I loathe (belief = reality) and knocked my socks off. I was earning a minor in Philosophy at the time, so it occupied a certain amount of my thought process. Sometimes, the Mage terminology slipped into papers I was writing for philosophy classes, which is a pretty good sign that they a) did their homework and b) hit their target.
Wraith: the Oblivion -- Honestly, I had to read this a couple of times to "get" it, but this game hit me in a spot very close to where Mage hit me. Maybe the theologic vs. the philosophic. So much potential. So few people interested.
Champions -- The first supers system I'd ever tried. Awesomely fun and incredibly flexible.
Fantasy Hero -- Listed separately from Champions because of how differently it played. I had one GM who pretty much copied Ars Magica with it. I had another that favored martial over magical heroes. I ran a game at a con that featured Far Realm type foes. One game I played had an cambion warlock; a "shaman" who only worked magic that affected souls; a gold-creating, clone-building, strength-augmenting high alchemist/transmuter wizard; and an incredibly skilled duelist with no magic. Each had a completely different way of representing their powers, played completely differently, and was totally balanced with the other characters. If I had just a couple more hours each week, this would be the one system I'd choose to play.
Aria -- A very different mold for fantasy roleplaying. I first picked up the Worlds book, which is probabaly the best guide I've ever seen for fleshing out incredibly deep settings and has rules for randomizing them. It also supports playing not just characters, but civilizations. The Roleplay book sucked me in immediately, too, but it ain't for the faint-hearted. It requires a thesaurus more than any other game I've ever played. It's also something of a meta-system used to flesh out character guidelines and a magic system in the same way the Worlds book fleshes out settings. I still think it could be the most outstanding game I've ever played... if I still had time like I did in school and had a group that was interested in immersive characters and settings.
Aces & Eights -- This game actually makes me want to play a western game and believe it could be fun for the long haul.
Savage Worlds -- Maybe not my top choice, all things being equal, but I don't think I'd ever complain about it. Quick, easy, and still comprehensive. When I teach my kids to game, it'll most likely be this, not D&D, that I start them with.
