I use a lot of free apps, but these are some that I have found to be very useful to me. Plus they haven't been mentioned all that much, if at all.
Colorcop - An indispensable tool if you build web pages or ever have the need to know what color something is.
XnView - A fabulous image viewer.
Exact Audio Copy
Avast Anti-Virus
Kerio Personal Firewall
CD Burner XP