Much appreciated. Thanks a lot.

Not a complete soundtrack, but a free track (Halloween) from the game Bully (aka Canis Canem Edit) on the official website.
That reminds me that Bully has one of the best soundtracks I've heard these years, really worth it.

Thank you. Note that if you use the EMUSIC link, you can download the whole soundtracks (".m3u" which means that you can listen to the musics as often as you want with winamp for instance, as long as the website is still up).

apparently you can listen to the entire overgrowth soundtrack from youtube: http://www.youtube.com/view_play_list?p=4F31EEBB6D2C4CFA

You can download the Overgrowth soundtracks from the composer's website. Thx Mikko Tamia, thx Weclock.

funny, I was asking the devs to put it up yesterday, and it looks like it is.
Also, I don't like 'em.

I finally added "Cave story" (I kept forgetting).

Not PC soundtracks, but if you like videogames sountracks, that's an awesome site about Zelda music.
Zelda Reorchestrated

Sounds like just fan stuff to me. Nice, but not really what you were listing for now. Maybe you could make a new part in your OP listing fan-made reorchestrations?

I'm just wondering if it's legal or not.

Your right, it's a fan site, not real soundtrack music site. But the music they reorchestrated is awesome.
I'm not a 100% sure, but I think it's legal. You have to take into account that there are a lot of stuff related to films and music made by fans (Lord Of The Rings fan made films for instance).

The fact that there is a lot of re-orchestrated soundtracks all around the internet doesn't mean it's legal. Maybe I'm wrong, but I assume that when you want to remix a song, the composer has to grant you permission. That would make sense to me.
But don't get me wrong, I'm not bitching about fan re-orchestrations. I enjoy them, and they usually do a good job. But since I want to keep this list as legal as possible...

You can download the complete in-game soundtrack to Ground Control at http://www.massive.se/gcdownload/ just scroll down the page a little and they are there.
Also, if anyone likes the Wipeout series (and the kind of music in them) you can download the soundtracks to Wipeout and Wipeout 2097/XL for free at Tim Wright's a.k.a CoLD SToRAGE website http://www.coldstorage.org.uk/
Plus many other games he wrote music for (mainly games by Psygnosis).

Wow, THIS is a great link, thanks: ;)
A lot of good things, including good old Amiga MODS!
(clic on "Archives" to access the download section)