I found this site, which scans your computer and tells you how many companies are tracking you, and they give you the option of "opting out" of tracking. I was surprised to see over 100 companies, most of which I never heard of, were tracking me. I opted out of all but two, which could not be accomplished for unknown reasons.
http://www.aboutads.info/choices/#completed
http://www.aboutads.info/choices/#completed