Just bought a pair of Urban Speak outdoor wireless speakers from www.rimax.net for our roof top here in Almerimar, Spain.
Usual set set up: base station, and battery or mains option on the speakers. They work as far as way as 20m (our roof not much bigger than that) and look like Darth Vedar! Bought them so that we could have the iPod/iPhone/iPad in the house out of the sun pumping out the content and place the speakers wherever it was shaded up on the roof.
Working a treat, very happy!