Anyone know the best or a good site to purchase a windmill to provide electricity for a single private home?A portable one would be better but any will do.

Have you checked the farm and feed stores in your area? If you have any in your area. Otherwise look online or in your yellow pages.

Here are some online sources:
American Windmills Home Page (http://www.windmills.net/)
Windmill Plans     www.fuelless.com (http://www.fuellesspower.com/windmills2.htm)
Brasada Windmills - Aermotor Windmills with Wood or Steel Towers (http://www.texaswindmills.com/index.htm)

Here are couple of additional sites for portable units:

Agriculture equipment, farm magazines, farm equipment, farm inventions, farm machinery, agriculture machinery (http://www.farmshow.com/issues/30/03/300307.asp)

WING - The Portable Windmill | GeekAlerts (http://www.geekalerts.com/wing-the-portable-windmill/)

Do a web search for "portable windmill".