I haven't gotten one yet, although I've considered both the Squeezebox and SoundBridge on occasion. You can actually get SlimServer (the Squeezebox software) to borrow directly from iTunes for playlists, and I think it will work with all or nearly all of the formats that iTunes rips discs to (including AAC according to the site) - so you should be able to just point SlimServer to your current files. You might want to download SlimServer and give it a whirl - you can set it up and even use a web interface to access it from another PC (the other PC basically mimics a Squeezebox).

Squeezebox seems to have become the successor to the old Audiotron as the most popular media player around - folks that have them seem to adore them.