This is a list of links that I've found useful that pertain to building or operating a greenhouse. I'll add more links as I find them.
FarmTek - a friend gave me one of FarmTek's catalogs and I've found more greenhouse supplies, shelters, and farm related stuff than I ever knew where to buy. I placed my first order on Saturday and it arrived three days later by semi truck. Yes, there were problems (wrong size plastic 24 x 100 instead of 32 x 100 and a missing part to a $145 wall inflation kit) and while I found that very disappointing, the lady at customer service was very helpful and I'm hoping this was just a bad beginning.
Sunny John Subterranean Heating and Cooling Systems - This site has a lot of useful information, some plans, and an on-line calculator to help plan a greenhouse utilizing subterranean heating and cooling technology.