Museek is a music player for Android phones. I highly recommend it.
→[More:] It's great for large music collections- you can browse your music on a visual "map" arranged by style, or use "smart shuffle" which tries to play songs that flow well into one another. I also like that you can add a song to the mix on the fly- your chosen song will play next, and then more random tracks will follow. Here's a
demo video that shows how some of this stuff looks.
Also, it's free. :) The app is still in beta, so there's an occasional hiccup (for instance, the "gapless playback" mode doesn't work yet on my G2) but overall, it's really a fun little toy, especially if you listen to your music on shuffle a lot.