There are a few different choices to stream music wirelessly to a central hub, but over at The Techman, Rui wanted a way to send music to specific speakers in his house, so he built in Wi-Fi capability to individual speakers.
Using an Arduino control board, a custom VLC engine and a WiFly shield, music can be streamed to individual speakers in different parts of the house. The open source software monitors the network for new speakers and the destination of the sound can be changed on the fly. The audio quality isn't the best, with streams stuck at only 32kbps, but it's mostly due to the modest hardware used. For full details on how to make your own, see the tutorial over at The Techman.