InstallWatch Pro from EpsilonSquared.
AvantBrowser — a good, free tabbed browser (followed closely by MyIE2).
MediaCenter V9 from J. River to keep track of and play my CDs and other music.
The Pine text-based email client from the University of Washington.
Cygwin to handle my Unix habit without requiring me to dual-boot any of my machines. I have curl, wget, SSH and X11 running on WinXP Pro.
CoolMon to keep me informed about what’s happening on my machine.
NetPerSec from PC Magazine/Ziff-Davis.
IrfanView, probably one of the greatest free image browsers around.