Some nice free software for Windows.

I have not tried to compile an absolutely extensive list of absolutely everything. I have tried to be selective.
I have used many of these programs on a regular basis, although, some of them I have just found but I do intend to use.
I suppose the bias on this list is towards creative and communications software, because that reflects my own bias.
Many of the programs are open source but by not all of them, quite a few are free for personal use versions of commercial software.

Web Browser

Firefox - Tabbed browsing from the ashes of Mozilla.
Opera - Now free.

Email

Thunderbird - Mail client from the ashes of Mozilla.

RSS Reader

RSS Owl - RSS feed aggregator.

FTP

Filezilla - FTP Client and server.

HTML editor

Nvu - Another program from the ashes of Mozilla.

"LAMP" for Windows

Xampp - Linux, Apache. MySQL, PHP - web development environment.

Telnet/SSH

Putty

Office tools

Open office - Office suite.
Dia - Diagram maker.
Open workbench - Project type program.
Free mind - Mind mapping software.

PDF

Acrobat Reader - Free but bloated from Acrobat.
Foxit Reader - Small, fast and free.
PDF creator (makes PDF's. Open office also allows export as PDFs).

Graphics

Win Gimp - Image editing.
Picasa - Image viewer.
Inkscape - Vector drawing.
Qcad - Computer Aided Design.
Scribus - Desktop Publishing (currently first Beta for Windows).

3d graphics

Blender - Cross platform 3d modeling.
Avimator - Avatar animation editor.

Moving image

Jahshaka - Promising, but not yet very polished.
Democracy - Video catcher and player (developing into an internet TV platform).
Video Lan - DVD player

Audio

Audacity - sound editor
Lame - mp3 codec (needed by Audacity to save projects as mp3s).
Juice - Pod catcher
CDex - Rip your CDs to MP3
Winamp - Many people are very fond of this player.

Misc Utilities

7zip - Like winzip, but free.
RealVNC - By the people who brought you VNC.
Spybot: Search and Destroy - Searches and destroys spyware.
AdAware Personal - Another Spyware search and destroyer.
AVG Free - Free Virus checker.
ClamWin - Free Open Source virus checker.
Kerio Personal Firewall - My free firewall of choice.
Net Stumbler - Find out what's in the ether.
Belarc Advisor - Find out what's on your PC.