Application to Avoid: Norton, McAfee, and other premium Antivirus suites
Indictment: Pricey, Slow, Bloated
Superior Alternative(s): Microsoft Security Essentials
Notes: Ever since Microsoft Security Essentials came out, you haven't had much of a reason to use anything else. MSE is lightweight, good at catching viruses, and does all of its work in the background without bugging you. If you really don't like MSE, though, you have a few other solid options, see link.