Waves are generally produced when wind blows over the sea producing a swell. In a sense, therefore, WavePower is actually a form of WindPower. The enormous size of the sea means that is a lot of Energy available whch could be extraced as WavePower.
There are a variety of techniques for extracting WavePower, mostly from systems close to shore. I'm also a fan of the notion of OffShoreWaveGenerators which seem somewhat underdeveloped at the moment.
The first commercial wave power system is about (Mar, 2006) to start production. This is a pelamis system; essentially this is a set of big tubes, with joints between them, which pump hydraulic fluid around. The system is being installed in Portugal, although the development work was done in the UK, and the system was built here, basically, because in Portugal you can charge somewhat more for wave power, than NonRenewable EnergySources.