Just ran across a post on a forum about making a solar hot air balloon, so I did some searching around..
http://www.solar-balloons.com has lots of good information about making your own solar hot air balloons, pre-built balloons you can buy from them, as well as videos and photos (some from the air!).
After that I ran across this news story about a blimp designed to hover in the same location at altitudes above 65,000 feet for up to a year at a time. Very interesting stuff. Apparently the blimp....
Do It Yourself Solar
