What's the latest in network music players, for streaming iTunes, MP3 files, and Internet radio throughout the house?

I learned a lot from this BBS back in 2003 about the Roku Soundbridge, Slingbox, etc. Moving forward to 2010, what are the latest devices and software for this task?

My goal is to use many little network music players with speakers attached (amp built in to the player) to replace analog radios in my house. Then, tune them to an iTunes library, web stream of a traditional radio station, iTunes audio stream, or folders of MP3 files.

In addition, I'm considering getting an iMac 27" to replace my 35 year old TV, using it as a media center for the house. Would network music players work with that?

Thanks!!