Groovefish will allow the most excellent Grooveshark music streaming service to be used on a Windows Mobile 6.x device.

Changes:

Completely rewritten code base for greater stability.
Huge improvements to the user interface, allowing search, browsing, and playing on one screen.
Search results now display the song and artist name.
Media player now allows for playing, pausing, and seeking the music stream.
Screen will no longer turn off while the application is running, ensuring the music won’t stop playing.

http://forum.xda-developers.com/showthread.php?t=561374