Heliocol Solar Pool Heating Systems:
www.heliocol.com

Goldline Controls:
http://www.goldlinecontrols.com/Products/Solar.aspx

Flasolar:
www.flasolar.com

Florida solar energy center:
http://www.fsec.ucf.edu/en/consumer/solar_hot_water/pools/index.htm

US Department of Energy, Solar Energy Technologies Program:
www.eere.energy.gov/solar/sh_basics_pool.html
www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic=13230

Canadian buyers guide to solar pool heating:
http://www.canren.gc.ca/prod_serv/index.asp?CaID=142

To quote from The Consumer Guide to Solar Energy