Centers for Disease Control and Prevention
Disability and Health Data System: Very data heavy.
Disability and Health: TONS of great and easy to use information. Very consumer health-y.
Disabilities & Functioning (Adult): This page provides a nice snapshot of "fast facts" along with the source of information which is usually a detailed PDF.
Disability Resources via The Department of Labor
Disability Resources: A list of government resources based on various topics (i.e. civil rights, housing, health, employment)
Cornell University: Institute on Employment & Disability
The World Health Organization
Health Topics -- Disabilities
The International Center for Disability
Disability Statistics & Policy in the USA and the World: A website with lots of links to agencies that collect disability statistics. Unfortunately, there are lots of dead links.