About.com: Does the MMR Vaccine Cause Autism?
Traces the controversy of the MMR (Mumps-Measles-Rubella) vaccine causing autism, first raised in 1998.
autism.about.com/od/causesofautism/a/MMRVaccine.htm
CDC: Vaccines and Autism Theory
Features various vaccines, their possible side effects, and research studies to determine whether a health problem is caused by a specific vaccine.
www.cdc.gov/vaccinesafety
Medinfo: MMR Vaccination
Summarizes reasons for having the vaccine and conditions where a link with it has been suggested.
www.medinfo.co.uk/immunisations/mmr.html