If you only need a single stereo output (eg. to connect to aux in), this is what I use:
It's still USB, but it doesn't use external power. Mine's connected to the aux in with a 3 inch 1/8"-RCA adapter, so there's not much room for noise to be introduced to the system.
If you look around you can probably find it cheaper than that site. I think mine was like $30 at Fry's.