Trackmania Nations Forever.

It's free on Steam, fun, good looking racer with online play.

Teewars - superb multi-player platfotmr/2D-shooter

If we're going to include Abandonware, then might as well include this...



Touhou Project is a series of danmaku games (bullet hell/curtain fire) games by a Japanese one man development team. A generally awesome alcoholic known only as ZUN does all the coding, composing, character art etc, somehow managing to pump them out at a rate of one game per year. They basically consists of little girls in weird outfits throwing several square acres of colourful orbs and lasers at each other. They're also the series mine and y-koron's avatars are from.

Wikipedia has a pretty good article about the games, but there's also a very nice Touhou Wiki just for them (frequently down these days), as well as a more honest one on Encyclopedia Dramatica.

4chan's /jp/ loves them too, but make sure not to mention them on /a/ or /v/.

Get them here for free.

Vista is killing me... a lot of these games won't work on them. Damn lack of full screen DOS mode!

RegnumOnline NOW. Fantastic free RvR MMORPG.

www.regnumonline.com/ar

Runescape, guys. Runescape.



...

 Played that for five years and don't really regret it. Was nice to play a game not based entirely on combat.

Less addictive than WoW seems to be as well, addicts only spend around 5 hours a day playing instead of 15. 

I think because there's already been a fair few flash game threads.

go here

Also, as for being stuck with only Vista, you have my condolences.   

 Actually, I agree entirely. The game's got a terrible reputation (and in many ways, rightly so), but it's a great concept and it's pretty fun, for the most part.

 I've played off-and-on since August of 2001. I joined two days before the Wilderness was introduced to the game. Haven't played yet in 2008 except to get the Easter item, though. I think I'm combat level 86 or something like that.