During the past couple of years I've become a really big fan of listening to instrumental soundtracks of movies and games while working on my computer (voices tend to be distracting while I'm writing). To this end, I've started buying soundtracks when they come on sale on sites like Amazon.com.
On the game soundtrack tip, I just wanted to point interested folks to a blog, http://gamemusic.wordpress.com/. The maintainer of said blog both discusses good commercially available game soundtracks, and also curates a list of freely available sountracks - mostly to classic PC games.
There are some real gems from a bygone era here: Homeworld, Daggerfall, System Shock 2, etc. Interestingly, it seems that many of these tracks were either made freely available by now defunct companies, or the composers retained the rights to the music and released it later themselves (some of the albums are actually enhanced or scored beyond the original say MIDI format). Check it out!