When I bought one 2 years ago, Pioneer seemed to have the best rep in my price range ($150-$200) and I went with the DEH-4600, which does MP3 and WMA files, and has a rear auxiliary input. It's treated me perfectly, no problems and very good sound.
The newer models (the 4700 I think) look pretty similar and are "ipod and xm/sirius ready" meaning I guess you just need the appropriate pioneer adapter. Crutchfield prices aren't great, but since you get all the installation gear and great support for free, I went with them.