I've been using
Clamwin on my flash drive. I'm rather disturbed by AVGs licensing model changes recently. 7.5 will be the last free version from what I can tell. I might just go with Clamwin on my main machine as it suits my style, low overhead, scans when I tell it to.
If you are going to pay then NOD32 and Sophos both come highly recommended.
Software firewalls are evil (never run two - never). That said... um I was going to recommend
Blackice, but it seems they're killing it next year.
Whatever you do, do not use Norton's firewall, it is truly evil - when the subscription expires it will not allow you to connect to anything on the web except Nortons subscription renewal site... enter your visa number please... I'm still amazed that they're allowed to get away with such extortion. I discovered this ugly fact on my stepfather's system - I recommended he backup, format and reinstall and never touch Norton again - he caved and paid them - I was disgusted. That is the ultimate Trojan.
The best firewall is user education.