PC Tools Firewall Plus Free Edition
Full user review
"Simple, clean, lean, mean Firewall machine!"
Very easy to use, efficient, takes up very few resources. Much better than Zone Alarm, which it replaced. Even works well on older computers with XP or not much RAM because it uses fewer computer resources to function.
None. No complaints.
For the beginner to the average to the experienced computer user, I highly recommend this Firewall. Most of all... it's FREE!!