My advice is to stay away from the low-end RF options. The sound quality is very bad and the reception is spotty. I like the WiFi idea and have been interested in doing this for some time but haven’t pulled the trigger yet.

Digital Networks: PC to Stereo. A new class of device that transmits music, photo and video files from the computer to home entertainment systems may play an important role as digital music and home networks really take off. [Wired News]