A friend pointed me to Sourcetone Interactive Radio, which offers a sort of New Age twist on Pandora. Sourcetone's main gimmick is a colorful mood wheel--select your mood by clicking on the wheel, and the service will begin streaming appropriate music.
There's a lot of verbiage on the site about how Sourcetone is basing its selections on scientific research, including some conducted by a team at the Beth Israel Deaconess Medical Center, but so far there's only one published research paper on the site. The scientific angle is not particularly interesting to me--any music fan knows that music can affect mood, and mood can affect health, so scientists are just catching up with human intuition.
Sourcetone's worthwhile because of the excellent music selections--mostly long instrumental tracks in genres like classical, avant-garde jazz, traditional, or ambient, including better-known artists like fusion group Shakti (which features guitarist John McLaughlin) and Yo Yo Ma, as well as more obscure independent acts like Married Couple. (I'd never heard of them and was pleasantly surprised.) They even threw in one of my favorite Otis Redding songs, "I've Been Loving You Too Long" under the Melancholy category. The sound quality was also surprisingly good for a streaming audio site.
Don't expect it to cure any diseases, but it might help you get through the day and turn you on to some interesting new music in the process.