I was reading the October '08 issue of Sport Compact Car and came across a mini-test of 3M Crystalline Automotive Window Film. It is almost completely CLEAR. It rejects 99.9% of UV rays and has a 1700+SPF. Chrystalline 70 transmits 68% of visible light and reduces solar heat by 38%. You can even use it on your windshield. I figure this would sure cut down on AC use, or keep things cooler without it. The mag's source for this stuff is:
Enter the World of Prescription Windshields.
Somebody must sell this stuff to the DIY crowd...or will.