In no particular order...

The GIMP
This is the finest image editor/manipulation program I have ever worked with. In fact, this is the program that I created most of the images on this site with (which is in no way indicitive of what it's actually capable of :D). It is GNU; it is free.

PSPad
The most awesome text editor I have ever used. Really.

WinRAR
Ever heard of Winzip? This is better. This is zipp'n magic. This is the mother of all things zip-a-riffic. It is free to try. Please do.

Mozilla Firefox
My browser of choice. I like it...and it is free. Of the tools here, I probably use this tool the most.

Diskeeper
What a fine hard drive defragmenter this piece of software is. I like it. I like it a lot. It's quite fast and does a splendid job. It's free to try. Try it.

Winamp
My favorite media player for a long time, now. It's free, too. That seems to be a recurring theme here, yeah? :) It's made better with plugins like Not So, Fatso! and SNESAmp. Beep beep, beepity beep. :D

Zone Alarm
My firewall of choice. It is frequently updated with more protection measures, quite easy to use, and it is free. Did I say it was free? Free is good. ;)