CDM is running a great article covering the current crop of DRM-free online music retailers. There are a few in their list I wasn’t aware of, but will certainly be looking into.
As both a creator and a consumer of music, I have a deep interest in this topic, and very strong feelings about it: namely, DRM sucks. I won’t go into all the short- and long-term issues with DRM, there’s plenty of reading to found via your friendly neighborhood search engine. If you don’t currently have an opinion on the matter, I’d encourage you to do some research and form one.
Speaking for myself, I don’t buy encumbered music, and while I haven’t released anything professionally, I can’t imagine that I would ever do so via a DRM-encumbered format or channel.