The Evo works pretty good with the Car Panel interface, direct link to music, navigation, and you can add your own custom links. I added Torque, so that displays most of the time. There are also various TV Show apps, and mp4 movies(for those in the passenger and/or back seat).

Low cost and basic installation...
+cheapo tape adapter
+usb extension
+headphone extension
+half of EVO case (2 small screws through panel)
+ELM Bluetooth Adapter
+Torque (from Android Market, not the most accurate for code reading, but 'live' readouts are great)