You want one of the dockable tuners, all of them have some sort of line out capability.  After that the prime factor is form factor and UI.  I prefer the look of the Clarion but the JVC and Audiovox are also good.  Also, if you have broadband at home, you don't need a tuner, all sirius subscribers can stream Sirius channels via the internet for free.
what's the best Sirius satellite radio to get?