When I worked with Python I installed the Enthought Python distribution (which I also happened to be the maintainer of, at the time): http://www.enthought.com/products/epd.php
Now that I work with Perl, I'd probably install Strawberry Perl.
Therefore I install the following: disable anti-virus warning, disable firewall + warnings, all updates, Firefox, Safari (also gets me Bonjour), One-click Ruby, Eclipse, Aptana Studio, Git (the msys port), Visual Studio 6 SP6.
Caveat: my latest Windows (XP) installs are in a VirtualBox VM.
after that, just the usual comfort foods; mingw, dev-cpp, emacs, and a few lisp dialects.
For me, its Vim, GNU Octave and Maxima, a few languages, Winsplit Revolution, and a few console tools (curl, mc, mplayer, unxutils, etc.,)
driver for samsung mfc was installed (never buy korean again, their hws are not friendly toward mac/unix), maybe gvim, putty and some other softwares
i didn't even install antivirus since i can just dd the hd again if it's acting weird. it's fair to say i don't use windows. it's there only for win-only hardwares which over time lose their significance.