I'm always asked what to use to fix your computer and ensure the computer runs great. Here is the list.
Prevention - Prevention is the cheapest and easiest way to protect yourself. Many products are free.
AntiVirus
Nod32 - Eset - Pay For AntiVirus
http://www.eset.com/
Symantec Corporate 10.0 (11.0 blows donkey nuts) (norton home products blow) - Have to steal as you have to buy multi-packs
Mcafee Corp - Lots of people get this free from work.
AVG Free - Free for home use but pretty shitty
Spyware/Ads Blocking
mvp's host file - free - blocks ads, bad web pages etc so you can't even get to them. simple hosts file.
http://www.mvps.org/winhelp2002/hosts.htm
Flash Block - free - Firefox extension that blocks flash. One of the best programs ever as Flash is worthless.
http://flashblock.mozdev.org/
Cleanup - Cleaning up the system is difficult, time consuming, and a serious pain in the ass. Should have prevented the problem from happening.
Spybot Search & Destroy (free) for spyware/adware (don't install tea-timer..it'll anoy you and you won't understand it)
http://www.safer-networking.org/en/home/index.html
Adaware (free) for spyware/adware
http://lavasoft.com/products/ad_aware_free.php
ccleaner - free - for cleaning up temp files, shit in the registry from useless old programs that were uninstalled.
http://www.ccleaner.com/
It's pretty much impossible for any of these programs to f*ck up your computer. Beware of CCleaner though...as it has powers to delete applications in evil ways. Just use the first 2 tabs on the left...and not the "programs" tab. Temp Files and Registry ONLY.