I use a Logitech Squeezebox Touch, $300. It can be run wired-only and that is, in fact, how I have mine set up.

You can connect a USB drive to it for storage, but most people store their music files on a PC or NAS. You then run a server app on the PC/NAS and stream the music to the Squeezebox.

There is a Wiki and a very active forum.

Axiom M80s + QS8s + VP180 <-- Pioneer VSX-1120-K <-- Squeezebox Touch / XBox360 / Oppo BDP-93