I just bought this JVC:
http://www.crutchfield.com/p_105KDR6...vc+600&tp=5684
Crutchfield includes the harness so you just twist together the wires and it's a piece of cake to install.
It has a usb slot, and aux in, plays mp3 data discs, cds, etc.. Just about everything you can throw at it. If you connect an ipod using the usb slot the headunit controls the ipod. If you connect it with the aux input the hu just handles volume.
I think is a great hu...especially tha ability to change the color of the face between like 25 dif colors. So I can make it match the red gauges or my green usb drive.
The next model up is about $20 more and add xm radio or something. Still under $200.