essential programs
When I get a new computer, what programs I need to put on it:
Standard apps (browser, e-mail, office, etc.)
Firefox
Thunderbird
OpenOffice
Trillian
BlitzIn
Development tools (programming languages, text editors, version control)
Perl, Python, Ruby, PHP
EditPlus (Crimson Editor, ConTEXT, and PSPad are also good alternatives)
jEdit (and a bunch of its plugins)
metapad (and replaced notepad with it)
Subversion and TortoiseSVN
MySQL plus the administrator and query browser
KDiff3
Proggy Fonts (Proggy Tiny)
The Regex Coach
Cygwin
Improved Windows Console (still early in development, but promising)
WitchEd
Network tools (protocols)
Ethereal
Putty
FileZilla
WinSCP
VNC
Viewers
Irfanview and all plugins (XnView and The Gimp can also be handy)
7-Zip (I also have to try ICEOWS)
Acrobat Reader
µTorrent OpenOffice downloaded in < 3:45 (!) with it.
iTunes, then uninstall the associated QuickTime, and install the Mega Codec Pack to replace it.
The K-Lite Mega Codec Pack, which includes Real Alternative, QuickTime Alternative, and The Divx codec.
The Ghostscript tools for viewing PostScript on Windows, particularly Ghostscript and GSView. See Obtaining Ghostscript, click through and you'll be able to download both Ghostscript and GSView.
Operating system enhancements/utilities
CLCL
TaskSwitchXP
XP Powertoys, particularly "Open Command Window Here" and "Tweak UI".
Free Launch Bar.
Some of the Sysinternals tools when I have a need for them.
Spacemonger when I later need to figure out what's eating up my space
Spybot and AdAware, eventually.
SlickRun is an excellent command-line style program launcher
Here are some automation utilities that may come in handy.