Otherpower.com
The cutting edge of lo-tec. Windmills built from scrapped airplanes, home made wood fired steam engines, battery maintenance advice etc.
Fieldlines
Otherpower's forum. Very hands on and useful
CirKits Links to Alternative Energy Web Sites
Probably the most extensive list of updated solar links
Build It Solar
Hand on DIY solar info
Solar PV Calculators
Useful tools to see what sort of stuff you need.
Space Heating
Solar Space Heating Overview on build it solar
One of the best collections of links
Aluminum Duct Collector
Air collectors like these can one the gist of how to build them. (most of the functional parts of this design can be scavenged)