alternative to Airtunes - Stuartli
The Sonos is reckoned to be the Daddy of them all, but my younger offspring has the Squeezebox (one produced by Slim Devices before Logitech took over the company) which performs splendidly.

He converted all his CDs to lossless files (FLV?) on his server and now plays music wirelessly through his hi-fi or wherever he wishes. See: for details and an illustration of the main panel.

The price in this review was from 2006 - it's now around £125 upwards. See: