AVG Free 2013 has received positive reviews and rankings on independent lab tests. The latest Webroot and Norton(I suppose) has also scored well but are around $40 per year. If you're trying to avoid firewalls, stay away from 'Internet Security Suite' software and look specifically for Anti-Virus.
The latest Bit-Defender scores were pretty good according to AV-TEST.
http://www.av-test.org/en/tests/home-user/producer/bitdefender/
The most effective thing you can do is keep your software, especially web browers+plugins(java, adobe *, etc) up to date and be mindful of the sites that you visit. Try running firefox, adblock, and NoScript if you're really concerned.