The computer version (XM PCR ~$50) displays all the songs currently playing on every channel.
It also has cool features like the ability to save favorite songs and artists and then notify you when that artist or song is playing on another channel.
One problem is that the XM PCR comes with a directional antenna that (in most areas) wont get good reception in a mobile enviroment. To overcome this problem I used the XM omnidirectional antenna that came with my stand-alone Delphi unit. Now my reception is always top notch. These omnidirectional antennas are available for purchase. I think they cost somewhere around $30.
I would definately recommend going with the XM PCR as oppose to using a stand alone unit.
We have three versions of XM radio tuners in my family, The RF modulator in my wifes car (she likes her stock radio) the ip bus connection on the Pioneer in my truck and the XMPCR in my BMW. By far, my favorite is the XMPCR. The software that is available is much much better than the tuning you can do with either the ipbus or the fm modulator hardware. I'm going to change my XMPCR install in my car so I can take it from the car and attach it to my multimedia PC in my tv room easily. Take a look at xmfan.com or this link right here will take you to the software developements going on.