In no particular order.

Pendragon Fucking lovely game and i still dig the supplements. Some really cool adventures. I'll have to get the new super campaign somewhen...

WFRP 1st & 2nd The career system was what first dragged me in. Then it started contributing food. Bonus!

Rolemaster I loved the choice in professions and quite possibly had my two best campaigns with it.

Ad&d 1st PLayed this for what, 15 years? Seems a bit limited these days, but i can't see all the fuss over the rules system. They're fine.

D&d 3rd Feeds my inner munchkin. If only Prestige classes were actually Prestige classes and not random collections of powers..

Rolemaster (any edition). I liked the flexibility of defense/offense inherent in the system and the fact that most fights end with critical hit results, not just hit point attrition. It makes combat more exciting.

Dragonquest I like the organization of the magical colleges and the lack of  rigid class/level structures. You can mix and match skills however you like. I like that armor absorbs damage rather than making it harder to hit someone. I like the spells being powered by fatigue points with a definite trade off between slinging spells and staying power in a fight.

Hackmaster Because it tickles my inner munchkin. is a hilarious read and is actually pretty playable if you are used to earlier versions of D&D.

Runequest It does an excellent job of presenting a "pre-medieval" or classical fantasy setting, and the emphasis on spirit driven magic makes for a nice change from other game systems.

D&D Because, well, it is almost a genre unto itself (especially the pre 3.0 versions).

D&D/AD&D - the 'common tongue' of RPGs.

Runequest - your character will get maimed, and probably die a messy death.

Elric/Stormbringer - your character will die, and probably have their soul obliterated, as well.

Tunnels & Trolls - fast-paced fun that refuses to take itself seriously.

Arduin - the original gonzo, over-the-top, on-crack game world/setting.

Runequest/Elric/Stormbringer I probably wouldn't run any of these in their default settings, but I like the overall BRP approach to fantasy--gritty, not strongly medieval, rooted in anthropology and history. I like the skill system in theory for getting away from the XP hunt; not sure how crazy I am about skill check bookkeeping in practice. I think I'll sneak Harnmaster in here, too, as it's similar in many ways to BRP with refinements to the injury system and a nice interaction between stats and skills. I think a homebrew combining Stormbringer and Harnmaster might be best of all.

The Fantasy Trip Wonderfully easy system to set up and run, and one of the few with high-powered "combat magic" that really balances magical attack & defense, along with regular fighters with bows & swords, into a complete tactical game. Also a very "complete" game with frameworks for magical item creation and character activity during off-times, not to mention a bunch of great solo adventures. Most of the game is set in an S&Sish world with a backstory of dimension-hopping Ancients, and thus there's room for a little bit of high tech if desired. One solo adventure, though, is based on Arthurian knights, and it does it very well.

Dragonquest a little more high medieval/renaissance feel to this rules set and (sketchily drawn) background. As others have noted, great magic system with a detailed college of summonings, and a character creation/development system that neatly balances the simplicity of classes with the detail of skills. Several of the published adventures also seem to be of high quality. (Natch, one is stolen from Shakespeare.)

Burning Wheel Provisional: the game has some elements which I haven't fully grokked yet. But there is much to love, from lifepath-based chargen (also found in various degrees in the BRP family above), to hero points that are earned in a nifty manner (though both earning and spending are a bit on the elaborate side), to combat and debate systems which, I'm willing to take on faith, are fun if you can figure them out.

Dungeons and Dragons Not by the books...but that's the idea of the game I'm thinking of, namely the original white box plus supplements, or the original three AD&D books. Too much there to make a good game if you include all of it, but judiciously edited...not to mention that the AD&D 1e DMG has so many good random tables. Make a dungeon, dive in...wander a city...trek through the wilderness...it's a world of wonder.

3. Ruinquest: cause it's groovy and strange and transplants from one setting to another pretty well.
2. Ad&D 1e cause it's generic and there are dwarves, halflings, gnomes and elves to kill.
1. Earthdawn- i like the mechanics waaay more than AD&D's. The funky way dice are used really did it for me and my group. my best campaign ever was done with this game. also there are dwarves, windlings and elves to kill.

I'm not a massive fan of fantasy games but let's see...

WFRP IMHO the essential dark fantasy RPG. V1 edges it in terms of background, whereas V2 has the edge in terms of rules

D&D Well, it's D&D! If you play that you're more than likely to get into a group in your local area

Rolemaster Could never understand the mechanics, but we had a guy who could GM an excellent session