M.K.
Wikipedia has a very well-researched article on this subject:
http://en.wikipedia.org/wiki/MMR_vaccine_controversy
I've read most of the sources quoted in the article; it also contains the most recent research on the subject. If you have any questions after the article I'd be happy to talk to you. After reading all the research, I went ahead and got my kids vaccinated. I don't think there is a link between the vaccine and autism for the general population and all of the studies I've seen support this conclusion. My sister has also read most of the research on this subject, and she opted for the MMR vaccine but decided to get it separately from any other vaccines (she asked her doctor not give her children polio, influenza, etc on the same day). Most doctors don't have a problem with this type of spread out vaccination schedule.
If you do decide not to vaccinate your son, do make sure you know the early signs of measles, mumps, and rubella since there are occasionally outbreaks in the US now that many parents do opt out of vaccinating their children.
Good luck making your decision, and feel free to send me a message if you'd like to discuss any aspect of the wikipedia article (or studies that are referenced in that article).