I recently tried Comodo Firewall on a few Win2K and XP boxes, and was impressed with what I found. I am a Network Security Engineer with quite a bit of experience with Corporate firewall systems, including FW1, Pix, and Linux based systems.
I used ZAP Pro for my own systems, particularly for those not behind a SPI equipped router. While it worked reasonably well, it was always a bit of a resource hog, and the overhead tended to adversely effect some applications.
I was looking for something with a simple interface, that would quickly configure itself, BUT would also allow for expert set rules (that followed 'typical' syntax of high-end FW systems). Comodo fit the spec nicely

I beat on Comodo FW with nmap for a few hours, and tried a wide variety of tricks and clever scans to see if I could get into the box in question.... Comodo performed perfectly, even with some of my custom rules configured.
Nice work guys, excellent FW all around. I'll definitely be recommending Comodo.
Thanks,
Griff