I am not just a Linux enthusiast, I also happen to use Windows quite often. In fact, Windows is my primary desktop from which I connect to all the other boxes and do my work on. During the years of Windows usage, I have accumulated a list of must-have Windows programs that I wouldn't be able to work without. Some of them are commercial, some are freeware, but that doesn't matter. What matters is how productive you are with your setup. If you're really productive on Linux with your own set of tools, it's perfectly fine and you have done a great job of finding the best tools of trade.
1. Total Commander.
I can't imagine working on a computer without Total Commander. Absolutely must-have software. Total Commander is what separates boys from men. Total Commander is probably the #1 reason why I don't use other operating system on my desktop. Tabs, a great GUI interface and customize-everything-configuration make it superior to all the other file managers. If I switch the desktop OS, I'll have to write my own clone of Total Commander or I wouldn't be able to work with the computer. Total commander is shareware.
2. TrueCrypt.
Because you don't want anyone to know what you store on your disks. TrueCrypt the best disk encryption software for Windows. TrueCrypt is freeware.
3. SecureCRT and Putty.
SecureCRT is the SSH client to use. Again, the primary reason I use it is because it has tab support. Putty comes second as it doesn't have tabs. SecureCRT is shareware. Putty is freeware.
4. WinSCP.
Forget all your FTP clients. FTP is dead and unsecure. I use WinSCP to send all my files over a secure connection. WinSCP is freeware.
5. Cygwin.
Since Windows has never had a usable shell, the only way to get one is to run a local ssh server via Cygwin and connect to localhost via SecureCRT. This way you get the best possible shell. Cygwin is freeware.
6. VMWare Workstation.
I have been using VMWare Workstation since 2004 and have never had a single problem. It's the best virtualization software ever written and nothing comes close. VMWare Workstation is shareware.
7. Synergy.
Synergy allows you to share your mouse and keyboard via network with other computers (no need for a KVM switch). It just works. Synergy is freeware.
8. Beyond compare.
The greatest visual diff tool ever written. Period. Beyond compare is shareware.
9. Tclock2.
Tclock2 is freeware that allows you to customize the windows clock in the systray. I set it to dddd\nyyyy.mm.dd\nhh:nn:ss.
10. Auto Hotkeys.
With Auto Hotkeys you can remap your keyboard and script shortcuts. For one, the first thing to do is to remap ESC to CAPS LOCK so that you could work in Vim. Auto Hotkeys is freeware.
11. Locate32.
Locate32 is to Windows what locate is to Linux. It helps you find all your files in an instant. Locate32 is freeware.
12. allSnap.
allSnap snaps your windows one next to each other, i.e., it aligns them nicely. allSnap is freeware.
13. Fineprint.
Fineprint is the best printer proxy ever. Allows you to print multiple pages per sheet even much more smartly than your printer does. Plus it has a real print preview. Fineprint is shareware.
14. Launchy.
I can't imagine working without Launchy. It's QuickSilver for Windows. It allows to quickly launch programs by pressing Alt+Space and typing in the first few chars of the program's name. Launchy is freeware.
15. ClipX.
ClipX maintains a paste buffer. Use Winkey+V to paste from it. If you haven't used it, it will change the way you work with your computer. ClipX is freeware.
16. DU Meter.
Du Meter measures your network usage and shows nice plots of it. I like it. Du Meter is shareware.
17. Taskbar Shuffle.
Taskbar Shuffle allows you to rearrange taskbar tabs and systray icons. Must-have. Taskbar Shuffle is freeware.
18. UltraMon.
If you're on a multi-screen setup, like me, UltraMon adds taskbars to your other screens. It's productivity super-booster. UltraMon is shareware.
19. Sumatra PDF.
Adobe Reader got bloated and died 5 years ago. Foxit Reader got bloated died 2 years ago. I hope Sumatra PDF reader doesn't die. Sumatra PDF is freeware.
20. KeePass.
KeePass is a secure password manager. I probably have 10 thousand passwords in it secured by one master password. Keepass is freeware.
21. RoboForm.
While KeePass keeps your passwords secure in a file, RoboForm allows you to dynamically submit them to various website forms. It also stores them under the master password. RoboForm is shareware.
22. WinRAR.
WinRAR is the best archivator for Windows. I have been using it since I was born. 7-Zip doesn't come close. WinRAR is shareware.
23. Inkscape.
Inkscape is a descent vector graphics editor. It's free.
24. FFDShow.
FFDShow is a codec library. If you want to watch all kinds of videos on your computer, it's a must-have. FFDShow is freeware.
25. Media Player Classic.
MPC is the best video player for windows. It doesn't have skins or any other useless bullshit. MPC is freeware.
26. Real Alternative.
Real Alternative will use Media Player Classic to play RealMedia files. Real Alternative is freeware.
27. Quicktime Alternative.
Quicktime Alternative is to QuickTime files what Real Alternative is to RealMedia files. Freeware.
28. AviSynth.
AviSynth is a video processing programming language. If you want to speed your videos up, it's a must-have. AviSynth is freeware.
29. FFMpeg.
FFMpeg is a must-have for converting videos and working with AviSynth scripts. FFMpeg is freeware.
30. VirtualDub.
VirtualDub is another must-have software for editing videos on Windows. VirtualDub is freeware.
31. Dependency Walker.
Sometimes programs don't work because of DLL hell. Dependency Walker helps you to diagnose and solve these problems. Dependency Walker is freeware.
32. Most of the Sysinternals tools.
Autoruns, regmon, procmon, procexp, tcpview, to name a few from Sysinternals are just must-have. They are all freeware.
33. File & Folder Unlocker.
UFFunlock is used when you get the nasty "Access denied" errors and you know that no process should be using the resource. FFunlock is freeware.
34. Hijackthis.
Hijackthis is necessary just to make sure you don't have nasty programs on your computer. Hijackthis is freeware.
35. ImgBurn.
ImgBurn is the new Nero. It burns your CDs and DVDs. ImgBurn is freeware.
36. IsoBuster.
IsoBuster knows all the CD/DVD image formats. IsoBuster is shareware.
37. Virtual CloneDrive.
Virtual CloneDrive allows you to mount ISOs right as windows drives. Virtual CloneDrive is freeware.
38. SQLyog.
As crappy as SQLyog is, it's somehow the most usable MySQL front-end. 10 years ago I used mysql-gui-console but the project got discontinued and no one has written a usable MySQL front-end ever since. If I'm ever in a mood, I'll write one that doesn't suck. SQLyog is shareware but I wouldn't pay a cent for it.
39. pgAdmin.
I applaud to pgAdmin dev team for making the best GUI front-end for PostgreSQL. Folks who write MySQL front-ends should learn from these guys. They know what a GUI tool should do. pgAdmin is freeware.
40. XML Notepad.
A notepad.exe for XML files. Allows you to edit XML smartly without destroying its structure accidentally. XML Notepad is freeware.
41. Hex Workshop.
Hex Workshop is a really great and easy to use Hex editor. It's shareware.
42. Vim.
For everything else.
What tools do you use?
This was a list of tools that I can't live without. What tools did I miss?