http://www.uscharterschools.org/pub/uscs_docs/index.htm - US Charter Schools
http://www.charterassociation.org/home.asp - California Charter Schools Association
http://www.magnet.edu/ - Magnet Schools of America
These are very general sites, but good places to start your research. Also, do a Google search for charter or magnet schools in your state. Most states have their own sites or associations. You can also go to the website for your public school district as these schools are usually under the supervision of the public school district.