Here is a short list of some reliable sources for information on vaccines, many of which were used in my latest series of posts on vaccination (I, II, III, and IV).
http://www.historyofvaccines.org/ - a site by the College of Physicians and Surgeons on vaccinations, their history and how they work.
http://www.cdc.gov/vaccines/ - CDC's website on vaccinations, the related illnesses and immunization schedules.
http://www.ncbi.nlm.nih.gov/pubmed - The NIH website that allows access to research peer-reviewed articles on a variety of topics, including vaccination.
http://www.asm.org/index.php/colloquium-program/browse-all-reports/91319-adultvaccinesfaq - information on adult vaccinations
http://www.vaccines.gov/ - Vaccine information about vaccine science, vaccine preventable illnesses and travel vaccines.