.NET related:
- Reflector (http://www.aisto.com/roeder/dotnet/): an excellent tool to view the source code from .NET assemblies.
- IE Developer Toolbar Beta (http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038): an IE add-on to view/edit page's DOM objects, JavaScript, CSS, etc.
- FireBug(http://www.joehewitt.com/software/firebug/): a FireFox add-on with similar functions of IE developer toolbar. You can debug JavaScript easily with latest version of 0.4.
- Fiddler (http://www.fiddlertool.com/): a traffic monitor tool to view all data transferred between your IE browser and a server.
- WinMerge (http://sourceforge.net/projects/winmerge/): a tool to compare and merge the files.
- NotePad++ (http://sourceforge.net/projects/notepad-plus/): a notepad that's much powerful than Microsoft's.