Free Tools: (probably most are mentioned already)
1.) Daemon Tools - Virtual DVD/CD drive for .iso, .bin/.cue, etc.
2.) Sasami 2k - Video Player. A little buggy, but nothing beats it IMO...
3.) Grabit - I used to be a Newsbin guy, but Grabit is my NNTP tool of choice now.
4.) AdAware - Clean those cookies, man.
5.) Mozilla 1.0 - Once you change, you just cannot go back...
6.) Motherboard Monitor - Keep those temps checked.
7.) Winamp - A given...
Pay Tools:
8.) ACDSee - Although I'm getting a little tired of it now.
9.) Nero - A no-brainer.
Really, not much else I use on a daily basis...
--Christopher