For home builts:
This is a practical size, and a proven design:
This is bigger, and not too many have been built:
Otherpower, mentioned above, is a good site. Home Power magazine has frequent articles on home-sized wind genrators. http://www.homepower.com/
I would say that anything under 1kw or under 8 to 10 foot blade diameter is a "toy" and the costs of a proper tower become a larger proportion of the cost of the system. Beware of anyone telling you that you can mount a wind machine on a roof.
I have been using a 1940s vintage Jacobs machine since 1978 or so. It has 14 foot diameter blades, and the generator itself weighs about 400 pounds. It is on a 60 foot tower, which is about 40 feet shorter than I would like. Also, our current location isn't as windy as the place we used to live, so we get 100 to 150 kw-hrs a month from the generator.
The tower and generator are another 250 feet up the hill from where the people in the picture are standing.