Advanced System Care - http://www.iobit.com/advancedsystemcareper.html
protect, repair, clean, and optimize your PC. With over 100 MILLION downloads since 2006, this fantastic, award-winning, free PC repair software is a "must-have" tool for your computer. 100% safe with no adware, spyware, or viruses; a PC maintenance program that's incredibly easy to use.
AVG Anti-Virus Free Edition 2011 - http://download.cnet.com/AVG-Anti-Virus-Free-Edition-2011/3000-2239_4-10320142.html?tag=main;productListing
Total Downloads: 363,398,516; Downloads last week: 1,344,355; Product Ranking: #1 in Antivirus Software
Secunia - http://secunia.com/vulnerability_scanning/personal
detect vulnerable and out-dated programs and plug-ins, which expose your PC to attacks