Trillian - without it, I'm isolated
XChat - when I do manage to get on the #tfp channel, XChat > Trillian's IRC support
AvantBrowser - I prefer it to MyIE2
BCDC++ - campus runs a DC hub, this is the best Windows-based client there is
WMP - Hate it all you like, but I prefer it to listen to MP3s with
SSH - Gotta manage my servers somehow.
Cygwin/WinGNU32 - Very useful to have *n?x command line utilities in Windows
Mathematica - I take notes in it, I do my homework in it, it's amazing.
Edited to add:
gVim - Best text editor ever (DOWN WITH EMACS)