The Belkin XM Radio Auto Antenna is supposed to improve the quality of your XM signal. According to the product description, Attaches to your car with its built-in magnetic base and offers a sturdy, weather-resistant design, with a 20-foot cable for positioning.
Also only on day left on AudioVox XpressR Holiday Bundle over at SRS. [...]

Pretty nice deal on a Satellite Radio package. You get a Delphi Roady XT Receiver, Car Kit, Home Kit, Home Speaker Dock, Portable Audio System, & $30 XM Service Gift Card for $99 from My Radio Store.
And here’s some reviews of the Delphi Roady XT Receiver.