What's a good low-resource firewall?

[DMoogle]

I used Sygate for a pretty long time before Symantec took it, but Norton is awful so I assume they ruined Sygate. Also, when I used Sygate and was transferring at high speeds (my internet speed is 5mb/2mb) it would cause noticeable lag on my computer, which isn't by any means fast (I'm using an AMD Athlon XP 2400+ with 512MB RAM and an NVidia GeForce 6200 A-LE graphics card with 256MB RAM).

So for the past few months I've been using ZoneAlarm. The lag when doing a lot of transferring is smaller, but still present. However, sometimes I get an error and ZoneAlarm shuts down and says I have to restart my computer. I have not discovered what exactly causes this, but it's a hassle.

So what are some other good, reliable, safe, and non-resource-hogging firewalls?