I can't recommend free software, but IMHO the best commercial av program is Computer Associates e-Trust Anti Virus. It is around $30, but the license allows you to protect 3 computers. It is what we use in the office machines, and we've never had a problem. The only time we did was on a laptop that the av had expired. http://www.ca.com or http://www.my-etrust.com.
I have been using Avast for quite some time now with no problems. You shouldn't have to pay for a program
Avast for your antivirus (register every 15 months)
SpywareBlaster for your spyware (free version, u run it and update as u use it)
Both for free and they use minimal resources so as not to slow your computer down
Hope this helps
In addition if you were to use FireFox as your browser instead of IE you may cut down on your viruses and spyware potential