Our MP3 Player Shopping Guide MP3 Players Rule just listed the cool Samsung Helix XM2Go live satellite portable radio and mp3 player.

The Samsung Helix XM2Go was announced at the CES 2006. Amazon.com has started to take pre-orders for the Samsung Helix. They charge you $399.99 for this portable satellite receiver and mp3 player. See also offers of other stores.
The Samsung Helix should ship by end of March.
The Samsung Helix XM2Go measures 3.7x2.2x0.6 inches and weighs 4.5 ounces. Besides listening to live XM satellite broadcasts on the go, the Helix can also record up to 50 hours of broadcast on its built-in flash memory and play MP3 and WMA music files.
The color screen has a size of 2.2 inch. A built-in FM transmitter allows you to listen to music on your car stereo.
A price-tag of $399.99 is not cheap, but the Samsung Helix is hot early adopter gadget. If you just want XM reception on the go, you still can just buy the rather low priced Delphi MyFi XM2Go.

Sirius Satellite radio has Howard Stern, but still is not able to offer a true portable receiver. The best you can get is the Sirius S50, which only receives satellite broadcasts when docked. I do not know what issues Sirius has with true portable satellite radio reception.