Zonealarm is getting on my last nerve

I'm ok with freeware occasionally popping up with ads during computer startup. I'm not ok when they keep trying to install stuff behind my back, and the stuff that gets installs messes with my programs, throws errors during Windows shutdown, and appears to be *unremovable*.

Anyone have any suggestions for alternative free firewall software that they recommend? There's always Windows Firewall and Symantec Firewall that I already have, but those tend offer somewhat less fine control over what gets blocked...