Here's my list (I put FR in brackets when the game was French so that the non-French readers understand why they've never heard of the game !)
Amber : I played once with another GM and although I loved the concept, I never had the guts to try GMing it myself. I guess I don't like to feel, as a GM, that I'm deciding the outcome of every situation. Randomness can be a nice element
Animonde (FR) : Weirdest RPG ever. I'm not even sure I read through all of it. Imagine a med-fan game with no violence and no combat system (more or less)
Blue Planet : Purchased it, read it, didn't like it, haven't sold it yet.
Chill : Bought it second hand for a laugh. Didn't make me laugh
Chimères (FR) : That was to be the apotheosis of the Hurlements RPG (see below). In effect, it killed the magic of not knowing what Hurlements was all about. Not that I ever GMed either game anyway, but I did play Hurlements a bit.
Over the Edge : Weird game also. Never figured out how to play with and what to run...
Donjon Clefs en Mains (FR) : RPG off-shoot of the famous French comic "Donjon" which talks about a dungeon, surprisingly enough. Not much point in RPGing it, I thought it would be a lot funnier.
Dream Park : I loved the VR idea and how you could really mess up your players' minds with this. Never got a chance to do it yet.
Dying Earth : I love Vance. I'm unlikely to run Dying Earth anytime soon, but it's a good read and full of nice ideas.
Ecryme (FR) : Jules Verne-esque alternate world, very reminiscent of the "Terres Obscures" comic series by Schuitten and Peeters. Dreadful game system, but nice setting and nice atmosphere. If I had time I would shift it to another system and then maybe want to run it.
Empire Galactique (FR) : Woohoo ! The first French SciFi RPG ever. Terrible in many ways, but I was actually proud to have that in my collection for a while...
Empires & Dynasties (FR) : One of the most original French RPGs. Imagine a Jorune-like atmosphere, a Pendragon like lineage system (you were only expected to play a given character a few times, then you'd play his descendent, etc.) with wonderful artwork and superb maps. Played it a few times, never got a chance to GM. Terrible system.
End (The) : Loved the concept, but ultimately, I think it's very limited in scope. Still, I enjoyed reading it.
Guildes (FR) : Original and yet accessible MedFan with a twist game. I bought it but, ultimately, I just want to play it, not GM it. So until I get the chance...
GURPS : I have a few GURPS supplements as "research material" for other campaigns : Scarlet Pimpernel, Voodoo, etc. Never read the core book, don't even own it.
Hurlements (FR) : Probably one of the best RPGs I ever played. The GM handles all the system aspect, and the characters are part of a wandering caravan of shapeshifters in Medieval France. Lots of mystery and stuff the players don't know. I collected all the supplements, but didn't read them on the off chance that I'd get to play them sometime. I'm stupid like that...
Hystoire de Fou (FR) : Bought it because it was Denis Gerfaud's second RPG. Denis Gerfaud is the author of the best French RPG (IMO, of course) Rêve de Dragon. Ultimately, Hystoire de Fou is just too weird though. It's kind of an RPG where you explore people's mental problems...
Immortal : Bought it as support material for Nephilim, lots of great ideas, but it never really got anywhere.
In Nomine Satanis / Magna Veritas (FR) : Got it because every French RPGer has got to have read this. Could be fun, but I never got a chance to try.
Judge Dredd : Man did I love that game... Unfortunately, the only people I knew in France who read Judge Dredd didn't think it would make a good RPG setting. Never had a chance to try it out...
Kult : Bought this at the height of my Vampire / Mage years, but it was just too depressing.
Miles Christi (FR) : One of the most historically accurate games I know, I bought it more as support material for Nephilim (again), since you play Templar Knights in the heyday of the crusades. Never actually played it.
Nobilis : Bought it coz' I like to check out new concepts. Fun, but I wouldn't find players willing to try it out.
Noir : I love Film Noir and thought it would be great to roleplay in such a setting. The game is nice, but ultimately, the genre requires lonely characters, which is hard to combine with the RPG experience.
Pendragon : Liked it, tried to convince a friend to run it for years, never managed to.
Psychosis : Wow ! I love this thing. I've always wanted to run it as a one-off "alternate roleplaying experience". Never got around to doing it.
Puppetland : That was included in an issue of Arcane. It was fun and tragic at the same time. Great game concept.
Sengoku : I bought it to supply a coherent setting and system to medieval japan. This book is a gem, but as with all historical games, I don't have time to put in all the work that is required to run a believable campaign anymore...
Space 1889 : Played a few times, loved the setting. I collected all the books over the years, but never got to run it or use any of the stuff.
Talislanta : Like some aspects of the game world, but never did anything with it beyond stealing ideas.
Trauma (FR) : The first modern non-fantasy game I played. Had a few nice sessions with it, but that was it.
Tribe 8 : Great game concept, superb supplements, enthralling story line, I guess I kept on buying the supplements just to know what was gonna happen. I don't think I'll ever have the courage to educate my players into this complex game world.
Wraith : the Oblivion : Bought it because it was part of the WoD games and I really liked the first three. But if Vampire was angst ridden and potentially tragic, this really was as depressing as hell. Never used it, never will.
Guess that's about it. If you guys want to see which games or systems I do use, check out
here