The Secret of Zir'An: A sturdy hardcover describing the world of Zir'An. The cover and the back blurb intrigued me, and I bought it on a whim. It's what would happen if you'd put Indiana Jones in a high magic setting. Interesting, but not really suited to my style of play.
(And if someone is interested, I'll gladly part with the book if it goes to a good home!)
Shadowrun, 1st edition: Got this close to when it came out. Played it a few times, liked the setting a lot but thought the mechanics were quite clunky.
The past years, I've played in a 4th edition Shadowrun campaign, but it's on hiatus right now (and I'm not sure it'll start up again).
Space Master: I got the 2nd edition. It's a straight science fiction port of the Rolemaster system, so it was only natural that I'd get it. I also have quite a few modules for it. I've played it a few times.
Fun fact: the planet Kulthea, the fantasy setting for Rolemaster's Shadow World modules, is on the Space Master map. And the systems are largely compatible, so you could mix and match if you would so choose.
Also, I really liked the 'Note on Measurements' at the front of the book: "It's all in metrics. Get with the program!" It makes sense that an advanced, space-faring civilisation would have abandoned the odd imperial measurement system long ago. ;)
Spookshow: A game about ghosts who get recruited by intelligence agencies. Think about it: they'd probably be quite interested in operatives that can become invisible and who can pass through walls.
Never played it though, it's not really my genre.
Star Wars: The West End Games edition. They put out a lot of sourcebooks for it too -- the only one I have is the Imperial Sourcebook, because I was interested in the organisational model used by the Empire.
I've played this only once, as a player in a satirical game. The Star Wars license has since been snapped up by other companies (FFG is putting out a trio of games for Star Wars currently), but this is the one that everyone played back then.
Sword of the Middle Kingdom: Wuxia game. Quite amusing, and you could do some pretty cool things with it, but Feng Shui turned out to be the category killer in that genre.
Never played it, but some of the mechanics could work quite well in an anime-inspired game...
The list of games I do not own but did play consists of only one item: Das Schwarze Auge, or rather the Dutch version of it: Oog Des Meesters ("The Master's Eye").
Recently, we've played through the first four modules put out for this. They're crazy in their own way, like featuring a ship with a solid hold, with dungeon rooms carved out... Good fun in an Old School way.
Would want to play:
Sagas of the Icelanders: I have a thing for Norse-themed RPGs. I tend to snap up the 'Viking'-supplements for games I have, even if I don't get any of the other supplements. And I've read some of the Icelandic Sagas, and liked them quite a bit. There's a lot of adventure in them. I've run a series of games at Ambercon UK where the PCs were Vikings, and the plots were inspired by both Norse myths and the Amber canon (like how Fafnir is guarding a Spikard, etcetera).
So I'd be interested to see how they deal with that in this game in their "more accurate historical approach [...] than is common in most games".
Sengoku: The 'warring states' period in the history of Japan is the inspiration of many games, anime and novels. I'm mostly interested in "the best historical reference material published outside of college textbooks".
And then use the system of Swords of the Middle Kingdom to run it as a total over-the-top romp, like in the Sengoku Basara anime.
Sorcerer: The subject matter does not really interest me. Exploring things about yourself through roleplaying is not my cup of tea: I want to be entertained by a game, not perform pseudo-psycho-analysis.
But Sorcerer is the game that almost single-handedly started the trend of so-called 'story games', and it would be interesting to go to the source of that, so to speak.
Summerland: Because of the intriguing setting.
Swansong: Shadow of the Prince of Darkness: Sounds really intense.
: RPGGeek is the best site for RPG enthousiasts. I've come to appreciate the community a lot, and it's a good source of up-to-date news like new releases.