First for .NET Development on windows:

1. NUnit – http://www.nunit.org
2. NCover
3. NCoverExplorer – http://www.kiwidude.com/dotnet/DownloadPage.html
4. NDoc SandCastle – http://www.codeplex.com/SHFB
5. ILMerge
6. Boo
7. SharpDevelop – http://www.icsharpcode.net/OpenSource/SD/
8. CastleProject
   

If I have to use Visual Studio, then I cannot live without:

1. CodeRush – words cannot do it justice
2. Refactor!Pro – words cannot do it justice
3. GhostDoc – inline xml comments the way they should be – http://www.roland-weigelt.de/ghostdoc/

General Windows Utils:

1. Cygwin
2. PuttyCyg – http://web.gccaz.edu/~medgar/puttycyg/
3. Notepad2 I use e-texteditor now I just use gvim now
   
4. Putty
5. UltraVNC
6. FireFox
7. Thurderbird
8. SlickRun (MagicWords)
9. Pidgin (GAIM)
10. WinMerge
11. Tortoise SVN
12. WireShark(Ethereal)
13. Windows Resource Kit (cdburn.exe is the best iso burner for windows)
14. Windows Support Tools are a must have for extra cmdline apps
15. 7zip
16. pdfcreator
17. gvim
18. Scanner - much like kde’s filelight

Firefox Extensions:

1. TabMix Plus
2. Web Developer
3. Greasemonkey
4. SessionSaver(if not on FF2.0)
5. Mozilla Archive Format
6. Reveal
7. del.icio.us
8. Dom Inspector
9. IE Tab
10. JavaScript Debugger
11. Total Validator
12. Performancing (best blog posting tool that I have found) I use LiveWritter now.
13. FireBug
14. FlashBlock
15. Resizable Form Fields
16. Adblock

Thurderbird Extension:

1. Plaxo
2. Nostalgy
3. Provider for Google Calendar
4. Lightning