I use Sonos but you can't be completely wireless unless you have speakers with batteries or run low power off a laptop. Ultimately a power source is necessary to drive the speakers.

Sonos does have 'wireless' speakers for streaming audio which are easily placeable anywhere with a power cable. You still need the base Sonos units for streaming.
http://www.sonos.com/shop/products/play3

"Those who preach the myths of audio are ignorant of truth."