You should use:
1. One resident AV with real-time protection, such as AVG.
2. At least a resident firewall. Either Comodo or Sygate are very good and not very resource intensive.
3. At least two resident Anti-spyware applications, preferably with some kind of real-time protection especially if you are not careful about your surfing habits. I prefer AVG-AS in combination with SuperAntispyware, but any listed in the Freeware Replacements topic have been used by our Members. I no longer use or recommend the new AdAware2007.
4. An alternate browser such as Opera or Firefox. The latter has add-ons that can supplement #3.
The above is courtesy of our Global Moderator, jgweed
Here is the link for Freeware Replacements For Common Commercial Apps