Xact's new Stream Jockey receiver for Sirius Satellite Radio can be used in your car or with your home stereo, but it also has the unprecendented ability to be used without being docked, as a walkman-style portable. The new antenna system is less fussy and can be used almost anywhere. HSN is carrying the Stream Jockey and the universal docking kit (home and car power adapters, antenna, and docking cradle) for $149.90 but to use it as a portable you'll need a battery pack that isn't available yet. Also, I'm not sure if you'll need a separate antenna too. More accessories will be released in the fall, including several compatible boomboxes.
Read the press release and the Sirius channel guide.