Sygate Personal Firewall (sygate.com) - Sygate offers the personal version of their firewall free for personal use. Go to the download menu and choose personal firewall.
Tiny Personal Firewall (tiny.com) - Tiny Software makes their firewall product free for personal use.
VCatch Virus Protection (vcatch.com) - VCatch works with major email clients, browsers and other Internet software to catch viruses before they can infect your computer. VCatch automatically updates whenever new virus signatures are released.
ZoneAlarm Personal(zonealarm.com)Firewall-Free security software to keep hackers and other maliciouspeople out of your computer. If you have an always-on Internet connection such as DSL or cable you should be using a personal firewall and this one is good and it's free.