I use a iphone 4 or the asus eeepad with local songs, then grooveshark for all the songs I don't have. Plus internet radio from both if needed.
The eeepad is great to hand around for people to choose songs, great with the guys when playing poker etc...
I use a Creative D100 bluetooth speaker (runs on batteries, or 12v/240v with adapter/s). This pairs to both and just a press of the button switches between them. Batteries have lasted over 20+ hours so far.
So much better than a dock, can have iphone in pocket 10+ metres from speaker, control volume, change songs etc..
http://au.store.creative.com/speakers/creative-d100/4-19228.aspx
The D100 is the best $100 I have spent for music listening related stuff. (besides this for the jeep http://www.usaspec.com/product.php?ProductID=21 )
Youngy