Comodo Firewall Pro
5 Star Protection, for Free. Includes firewall, anti-rootkit, anti-virus protection, completely stealths your pc from hackers.
I use comodo, and it's pretty darn good. Less system load, and a faster scanner than AVG. I was an avg free junkie for a while, until I found Comodo.
I'd also like to recommend using
Spywareblaster
This program will block harmful sites/ips and software from installing itself on your PC. You can also lock your hosts file to protect it from being modified by browser hijackers.
Also, use the Immunize function found in
Spybot- Search & Destroy. This program is also a good anti-greyware scanner, also finds dialers, rootkits, trojans, and bots. Free.
Ad-Aware 2008 Free is another good anti-malware scanner.
If in doubt, run the scanners in safe mode, since many viruses can't latch on to vital system processes if they're not running, and you'll get a better chance of success removing them in the case of a severe infection.
And for you Advanced Users (
I MEAN IT! This can BREAK your PC if you don't know what you're doing!) You can use
Trend Micro's Hijackthis to remove stubborn malicious greyware appearing at start-up, malicious homepage hijackers, and more. Very powerful, so treat it like a double-edged sword.
I also recommend
Eusing's Free Registry Cleaner to optimize your PC's registry (important).
Additional Anti-trojan program also good to use, is
A-Squared Free.
If you need a good process monitor (other than task-manager) to end stubborn virus processes, check out
Sysinternal's Free process manager.