Here's some stuff that I find useful. Maybe you will too, who knows.
AVG from Grisoft
AVG Anti-Virus Free Edition is a free anti-virus protection tool developed by GRISOFT for home use.
Cost: Free!!! (Comment from Chris: "Works better than Norton or McAfee")
Ad-aware from Lavasoft
This program finds spyware. These are small programs that advertising companies place on our computers. They report back on our browsing habits. Run Ad-aware weekly, and get this garbage off your hard drive.
Cost: Free!!!
SpyBot search and destroy from S&D
Detects and removes spyware. I use it along with Ad-aware for keeping the garbage off my computer.
Cost: Free!!!
Window Washer from Webroot Software
Clean up your web browsing tracks and rid your computer of cookies and unwanted items that clog up system resources.
Type: Free to try
Cost: about 30 bucks.
Registry Mechanic from PC Tools Software
Safely clean, repair and optimize the Windows registry.
Type: Free to try (unregistered version only corrects a few entries)
Cost: about 30 bucks
PerfectDisk® From Raxco Software
Fast and thorough disk defragmentation, optimization and free space consolidation.
Cost: Starts at 40 bucks but it's worth the money. It seems to work well.
RegClean from Microsoft
RegClean is a small application that will save a lot of start-up time. It clears the Windows 95/98 Registry safely and effectively. With the Registry cleaned out, you'll have a shorter wait when you boot the computer.
Cost: Free!!!
SG TCP Optimizer from Speedguide.net
The TCP Optimizer is a free, easy Windows program that provides an intuitive interface for tuning and optimizing your Internet connection. There is no installation required, just download and run.
Cost: Free!!!