I've played in several different types of games. Due to the wealth of support for 3.0/3.5, I pretty much stick with it now but back in the day....
Fantasy Hero: I used the setting from the main book in addition to Shadow World.
Rolemaster: I GMed a Forgotten Realms campaign where the characters were in the south, Calisham all the way! Inspired in part by the various Tiger and Del stories or Sword Dancer series.
Warhammer FRPG: Ah, nothing quite says "I am naked and unkillable" as a dwarven giant slayer.
Talislanta: Want something truly different? THis is it. This, way before Dark Sun and Planescape, showed me how much art mattered to an RPG in setting tone and style. Great stuff.
Mage: They had a system out called the Sorcerer's Crusade. I even wrote an article on piracy for Pyramid on that era and game system. Good stuff overall.
Ars Magica: Never got into this one much. Loved the background, maps, and well, richness of tone.
L5R: I played the original a lot. For some reason, we all seemed to wind up Ronin at the end...
Palladium Fantasy: It was D&D with steroids. What else can I say? Of course quite a lot of that material, including even the campaign world at one point, was used for a D&D campaign. Some of their sourcebooks are really great. I especially enjoyed the Wolfen Empire and the Western Empire. Great stuff in both books. Bill Coffin was a great author for them.
Stormbringer/Hawkmoon: Interesting system but the ability to get killed in a single blow at times just made me shudder and usually pass on it. Not too bad if you've got the demon bound goods mind you but wtf, they're on like the 6th edition or something and people cry about 3.5.
GURPS Fantasy & Fantasy II: It's going to sound strange, but I never knew what Fantasy II was making fun of until I got older and then it hit me. The first book was okay, but if it had been like GURPS Space, just a massive genre book, instead of an okay setting/genre book, it would've rocked. Haven't played in a long time that one.
There are some systems I'm in the middle of like Deathstalkers, HARP, Victoriana but mostly, it's just D&D. I can do pretty much all I want with that one system now. Both Grim Tales and Conan look to add new layers to the system and I'm kinda excited about Unearthed Arcana and the various Player's Guides coming out next year.