I've long been an advocate of using music for background in D&D. A ways back I started the RPG Music Project to collect a listing of CDs that worked well with RPGs, there's a list of more than 50 available at
The RPG Music Project. Mostly movie music because shorter, more emotionally pointed pieces that are used in movie scores tend to lend themselves to gaming better than classical pieces that may change mood mid-movement, or pop/rock music that tends to be more distracting.
Also monte cook has a couple of lists of music
here and
here. I've found his lists to be quite good. You can find a few articles on using music aside from the Dragon article at
roleplayingtips.com, and this
article by scott waisner.
My biggest tip is that if you want to use music in your game, take the extra effort to make a compilation for each mood. Single-mood music goes much further to adding ambience than music that switches moods from song to song. I mean, nobody wants to hear something soft and sweet in the middle of battle. Carl Orff's Carmina Burana has a great first (and last, they're practically the same) movement, and a couple other good battle-ish movements, but some of the other movements are just way too frilly. Then if the mood of the moment changes, you just change music.
Some ideas for how exactly to do this are:
1) use your computer to make separate MP3 playlists from your various recordings, divided by mood. Of course, then you have to play in the same room as your computer.
2) burn CDs with each mood. if you have a multi-disk changer to play them back on this is best, cause otherwise you have to change CDs when you should just be gaming.