I'm not big on Soundtracks, so I don't know how good they are personally, but the
Jeremy Soule website CD section lists 2 Soundtracks for Guild Wars and 1 for Dungeon Siege II listed there. On
DirectSong, apparently the official source for any of his music, there are 4 Guild Wars soundtracks, 2 for Prey, Dungeon Siege II, Warhammer - Mark of Chaos, Supreme Commander, Oblivion, and Morrowind.
If you're not a big fan of his battle music, you might want to check out Prey first and then maybe some of the Guild Wars soundtracks have non-battle music. There are a few sample tracks for each album right on the website.
I like the idea they had for Expansion Packs just for the music of the games. It would be cool to add "Official" new music to a game to spice it up. Unfortunately, they only have one for Guild Wars. If they were going to do an add-on for Oblivion, it would have come out much closer to the release of the last of the Official expansions or maybe even with GOTY. By now, the market isn't exactly ripe for selling lots of Oblivion add-on music.... not to mention that with the ease of modding they'd probably sell even less with modder-pirates simply passing copies of the mod around under different names or mixed with their own content.