McAfee VirusScan Plus 2009 Edition for free shipped after a $40 rebate. Here is a screenshot for your reference. It helps shielding PCs from viruses, spyware, and has a firewall to protect against network attacks. It also features McAfee SiteAdvisor, an online safety guide that warns about risky web sites before users visit them. You may also want to check out this deal. Most places have antivirus program for over $30.
Originally posted earlier, this is just a friendly reminder.