Best paid for is ESET Smart Security, which includes a strong firewall and the best anti-virus on the market, or save your money and use the software below:
http://www.download.com/ESET-Smart-Security/3000-2239_4-10807868.html
Quality free internet security for XP and Vista (32 and 64 bit):
You can protect you PC very effectively for free, you should always have firewall and anti-virus software installed and running before browsing the net, as well as scanning you PC with additional anti-spyware software once a week, You can get all the quality security software you need completely free, these are often better then the paid for software like Norton and Mcafee, below are links to excellent free software, download and use all 5 to fully protect your PC.
Avast Anti-Virus Home Edition
http://www.avast.com/eng/avast_4_home.html
Comodo Pro 3 Firewall
http://www.personalfirewall.comodo.com/
Malwarebytes:
http://www.malwarebytes.org/mbam.php
Firefox 3:
http://www.mozilla.com
WOT (web of trust) Add-On:
http://www.mywot.com/
Install the WOT add-on it is a free internet security add-on for your browser. It will keep you safe from online scams, identity theft, spyware, spam, viruses and unreliable shopping sites. WOT warns you before you interact with a risky website. It's easy and it's free.