As far as music streamers go, Logitech's new Transporter is one of the sexiest we've seen (and also the most expensive). The $1,999 system claims it can deliver an "audiophile" worthy performance whether it's streaming from your PC, the Internet or an online service. It connects to the Internet via Ethernet or wirelessly and comes with both analog and digital interfaces on the backside.
It works with Macs and PCs and unlike other streamers it doesn't limit you to one Internet station. That still doesn't make it worth $2k, so unless you have the cash lying around, you could find less expensive streamers that get the job done (and do video as well, which the Transporter doesn't).
AU: Not sure where this was sourced, but the Transporter has been around since at least last year, maybe 2005, from Slim Devices, along with their more reasonably priced streamer, the Squeezebox. Logitech bought these guys out last year, so perhaps that transition is now wrapping up and word is spreading on their great gear. Wicked Digital sells the Transporter locally for $2999, and Squeezebox is $499, but also available for $489 from Frequency.