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In that order...
I use McAfee viruscan and firewall. I also use a router. I keep up with Microsoft updates.
I will visit any site without fear - even if I know they are trying to load a trojan on my computer. I cannot even remember the last time I had something "bad" on my computer. On the other hand, I just had someone at work ask me for help (he gets pop ups all the time.)
Having said that, what you are already doing and the ones that BillyS has suggested should probably be OK.
Spybot S&D - trojans
AVG - virus
Sunbelt Kerio Personal Firewall
All have free personal versions.
you should consider the consequences of a system failure and balance this against what it costs annually for something likeNorton System Works.
If you've ever worked in the support industry, you'll quickly realize that Norton's products are the cause of the "problems" they detect ;)