General Adapted Physical Activity sites:

American Association of Adapted Sports Programs  - http://www.adaptedsports.org

Adapted Physical Education Guidelines - http://www.cde.ca.gov/spbranch/sed/APE/index.htm  
Adapted Physical Education Advocacy Page - http://www.mankato.msus.edu/dept/colahn/APE/APEpage.html
Adapted Physical Education National Standards - http://www.cortland.edu/APENS/examapgeneral.htm  
Adapted Physical Education National Standards - http://www.twu.edu/apens  
Recreation Resources for Individuals with Disabilities - http://www.familyvillage.wisc.edu/recreat.htm

 Specific Disabilities:  

Autism Speaks: http://www.autismspeaks.org/index2.php  
Visual Impairments - http://www.campabilities.org/tvic‑index.htm

Down Syndrome: http://ds-health.com/
United Cerebral Palsy: http://www.ucp.org/