This depends on WHERE you live.
For the U.S. I highly recommend HD radio (Directed or Visteon using Mitch's board) -- this is what most people use and what most people suggest.
If you don't want to spend that much, then second best I would highly suggest the Silabs USB FM tuner. Very small, simple, much cheaper and still has RDS support.
Radiator Support has been removed following from trends on this poll (which lists the current support):
I would try to stay away from WinTV for radio. The current implementation is made to work with this application: http://www.hauppauge.com/html/radio.htm but I have reports that the seek function is not working entirely as expected. In any case, if the card works with this application it should work (for the most part) with RR.
US: I have not heard good things about any ATSC (HDTV) tuner for in-car use.
Europe: I would suggest a Diversity Tuner like Cinergy USB Diversity stick -- I doubt anything else will have better reception while moving.
If you live in Europe, you may be able to listen to digital radio with the TV (DVB) card as well (they're just a TV channel with audio only).
You may have to embed the manufacturers application for digital TV, or try to use the Winamp TV plugin (which may work for a lot of cards).
For Analog TV you can pretty much use any card and use the Winamp TV plugin.