Aside from the widely known ZoneAlarm, I've heard something about Online Armor Free Edition (albeit from PC World Magazine...) which may suit the end user needs of a guru who wants to lock the door on a cute looking girl- er, I mean PC.
I haven't really used a firewall on my computer in a long time (and likely due to the lack of travelling to strange sites) so I don't know which of the two to recommend.
