AVG- AntiVirus

AVG Anti-Virus Free Edition is the most popular free solution available at no cost to home users and provides the high level of detection capability that millions of users around the world trust to protect their computers.

http://free.grisoft.com/doc/5390/us/frt/0?prd=aff

 Ad-Aware – Anti Spyware

Ad-Aware 2007 Free remains the most popular anti-spyware product for computer users around the world, with nearly one million downloads every week. Our free anti-spyware version provides you with advanced protection against spyware that secretly attaches and takes control of your computer, resulting in aggressive advertising pop-ups, sluggish computer activity, even identity theft through stolen bank details, passwords, and credit card account numbers.

http://www.lavasoftusa.com/products/ad_aware_free.php