I believe a mix of the leading products (Avira, Avast, Nod32, Kaspersky, McAfee, Norton, Malwarebytes, AdAware, SpuBot) are good solutions whether you buy them or get the FREE versions. The core engines of these products take care of viruses, adware or spyware or malware exceptionally well. You just have to pick which ones do what...
FIRST, for ANTI-VIRUS, I would recommend Avira which is FREE: Avira Antivir Personal: http://download.cnet.com/Avira-AntiVir-Personal-Free-Antivirus/3000-2239_4-10322935.html
A good BUY anti-virus/anti-malware product is Kaspersky: http://download.cnet.com/Kaspersky-Internet-Security/3000-2239_4-10012072.html
You can also try, for FREE, Avast as an alternative anti-virus solution:
Avast 4 Home: http://download.cnet.com/Avast-Home-Edition/3000-2239_4-10019223.html
Avira's Antivir has a detection rate of over 99%, includes "root-kit" protection, and uses less system resources. Avast detection rate is around 97.8% and includes "root-kit" protection. Avast Anti-Virus is good if people suggest that, Avira is just slightly better.
Kaspersky, Nod32, McAfee and Norton are high up on the same list with Avira, Avast, etc…) You could try AVG, but AVG’s detection rate is less than 85% for Script Malware and General Malware, and does NOT include "root-kit" protection in the FREE version…
Here's a good report (Feb 2009) on many of the top AV (anti-virus) products.
http://www.av-comparatives.org/images/stories/test/ondret/avc_report21.pdf
Avira came out as one of the top AV products in the testing. AVG was not nearly as high mainly due to AVG NOT detecting a lot of Script Malware and General Malware problems in the tests, plus, slower scan speeds and a higher number of "false positives".
SECOND, also make sure you have the right mix of product(s) so you have BOTH
ANTI-VIRUS AND ANTI-SPYWARE/MALWARE software running on your computer.
A good FREE mix could be Avira and Malwarebytes, with McAfee Site Advisor (FREE) installed as well. Avira Antivir Personal: http://download.cnet.com/Avira-AntiVir-Personal-Free-Antivirus/3000-2239_4-10322935.html - Malwarebytes - http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html
Or, a good BUY/FREE mix could be Kaspersky and AdAware (or Malwarebytes), with McAfee Site Advisor.
Kaspersky: http://download.cnet.com/Kaspersky-Internet-Security/3000-2239_4-10012072.html
Ad-Aware - http://download.cnet.com/Ad-Aware-Anniversary-Edition/3000-8022_4-10045910.html
Hopefully, you get my main points of core features AND the mix of solutions. You just have to get those 2 things right and you're covered!