I cast my vote for Antivir. It detects any suspiscous file before I even open it, yet never seems to hinder performance (even in doom3). As for firewalls, I used to use Kerio 4.2 but switched back to v2.1.5. It lacks app monitoring, which can be an annoyance during installs but can help you catch spyware installs if you're not paying attention.
Grafik : BTW... Kerio still operates after the demo is over, just minus a few features. For a pop-up blocker, I'd recommend firefox. It's all built in, and allows you to set allowances if necessary. Couple it with NoScript and AdBlock and goodbye ads forever. Otherwise, Kerio has a built-in adblocker (problematic) and the msn toolbar for IE adds pop-blocking (which I believe is in the new IE anyways) and tabs I believe.