Security Software

Best antivirus, antispyware, and just antimalware in general.

     Just doing a bit of research on my own to figure out what antivirus programs I want to use once I do a clean install of Windows 7 on my laptop.  Obviously, I cannot personally try them all, so I'm going to be listing ones I find most mentioned and in general what people say about them.

Free Antivirus Software

Avast (Free) - Solid antivirus with high detection.  Long reputation.
Avira (Free Edition) - Simple user interface.  Started out especially strong in 2008.  Solid virus detection, on par with Avast, but tends to have false alarms (false positives) as a reputation.
Microsoft Security Essentials (MSE) - Very lightweight, almost "invisible." Detects as much viruses and malware as any of the others and getting consistently good reviews; however it is fairly new so it might be too early to judge.  Much concern over the fact this is Microsoft, but another argument could be it is in Microsoft's own best interest to make sure PCs become reputably more secure.
*Updated 2011: Unfortunately, can't recommend this anymore.  Was running MSE on my laptop and Norton on another; twice this year the laptop got infected and had to clean by scanning with the Norton software instead.

Free Anti-Malware

Malwarebytes Anti-Malware
Microsoft Security Essentials (MSE) - See above.
SuperAntispyware

Misc. Free Tools

MBRCheck - Checks a drive for corrupted master-boot-records.  Useful if your computer isn't booting up and you can take out the drive to check on another computer.

Commercial Antivirus Software

Norton Internet Security - Used to be a system hog but it's improved a lot since the 2009 version.  Use it primarily now; have never had a virus on the computer this was installed on.
ESET Nod32 - Lightweight, supposedly gaining stronger repuation last few years.
Kaspersky - Full featured, heavy-duty.  Not light but very robust.