I'll avoid the comments about Apple and Linux to avoid a flame war.
But as for the question asked...if you want to spend a bit of money, one of the best anti-virus programs on the market is Kaspersky and it is also one of the lowest priced. Stay far away from Norton and McAfee products. They are bloated and overly problematic. If you want a free solution I would go with Avast.
Personally I don't like the security suites and find that most users have no need of them, and the messages they tend to frequently pop up with are generally beyond most users ability to understand. If you are using a router, and everyone with a high speed connection should be, the Windows firewall should be all the protection you need. If you are already having a problem with a malware infection, one of the best things to download and run is called Smitfraud fix. Many of the worst malware floating around are variations of either smitfraud or Vundo and this tool will remove both of those problems.
When it comes to spyware protection, the two best on the market today are SuperAntispyware and Malwarebytes AntiMalware. Both have free versions that can be downloaded from
www.download.com I would recommend using both of them to scan your system as no program will catch everything that is out there. Be aware that the free versions do not provide real time protection and you will have to do regular scans to protect your system. And to achieve the best results, scans should be done in safe mode after turning off the system restore function in Windows. Some malware have the ability to hide in the system restore area and will reinfect your system after it has been cleaned.
One thing I will mention is that Vista is very secure against malware and virus problems. I have been running a Vista system with no real time protection for over a year and surfing the typical sites where you will become infected and have had no problems. I service computers for a living and have had only two malware problems on Vista systems, both caused by the user installing the malware against the UAC warnings that Vista gave them.
Basically the old rules still apply: do not open e-mail unless you know the sender and even then be careful. Use a web based e-mail program instead of your ISP e-mail account as they have good integrated virus protection.
When downloading, use torrent and not a p2p program like Kazaa or other similar programs and download torrents from reliable trackers such as mininova or piratebay. Be aware that many cracks for software and games are infected with trojans and proceed accordingly.
It's not as bad as many people like to portray. Most people have no problems with malware if they have a good AV program and anti spyware.
Oh yeah...one note on Apple that I just can't resist... Apple released a bulletin that all users should have at least one and preferably two anti-virus programs installed on their systems. Apple products are not inherently secure against virus attacks any more than Windows systems are. It's just that no one bothers to attack them. That may be changing.
Techman