Beware of the cheap ones. A windmill has to be strong enough to handle extreme weather conditions. It is my understanding that Bergy makes some of the best ones.

http://www.bergey.com/

John

Here is a link that might be useful: Bergy Windpower

Before you buy, check your municipal code. Your town may frown upon erecting a tower. I saw the result of that about 1 mile from my house. A family put up a $10,000 system without a permit. The town inspector got miffed and forced them to move the rig 100 ft away from the front of their property - and buy a permit to boot. The new location was behind the house and down an embankment. It lowered the generator several feet below its original site and the drop in wind speed removed any economy it may have had. The result was the owner took down the generator and the bare tower yet stands. It's been that way for 20 years. He was out $10,000, but got experience which does not generate electricity. He could have bought a "winter beater commuter" car for that price.

The best use he got out of the tower was for a giant lightening rod.