When my group used to game together in person (well, they still do, I'm the only one sitting behind a webcam eye) I played soundtracks in the background that went along with the game.
I'm a huge fan of dungeon crawlers, so I picked music that would enhance the mood. The OST to Shin Megami Tensei: Digital Devil Saga is perhaps one of the greatest ones I've ever listened to. It has a lot of ambient soundtracks that are perfect for tense situations or for a good dungeon delve, and some rocking battle music and town themes for when things need to be spiced up or toned down. I'd also suggest the soundtrack to SMT: Strange Journey now that I've gotten a chance to listen to it.
The soundtrack to Final Fantasy VII is also a great one to play if you pick and choose the songs. It has tons of tense music that is perfect for a dungeon crawl, as well as some decent songs for other situations, though those tend to be nothing spectacular.
I'm not sure if anyone specifically produces music for use in RPGs. I do know that there have been some collections released for that purpose, however. If the music was good, and better than what I hear on a regular basis in different media, then perhaps I would purchase such a thing. But if it's subpar compared to a Star Wars OST that I can download, is it really worth my time and money?