Have you ever wanted to record a video of what is happening on your computer screen? There is a free program to do called AviScreen it that works very well. I use it to make better presentations at work.
Some other useful programs are Neat Image, to remove noise (aka "grain") from images and Superbot, to download an entire website at once. To get rid of spyware, I recommend Spybot.
If you want to know what's taking space up on your hard drive, try WinDirStat.
Let me know what other things you want to do, and I'll tell you what free software is out there. I've tried a lot of it.