As far as head units with built in XM tuners, AFAIK there are none currently in production... Alpine used to make one, but it's out of production.
If you buy a head unit with built in XM controls, however, you only need the tuner itself (as opposed to the entire control unit). Look at the XMD-1000 tuner; it can be placed anywhere since it uses the controls on the head unit. I don't know specifically what head units can control the XMD-1000, but they shouldn't be too hard to find.