Must-Have Web Development Tools

• IEDevToolbar (like FF's Web Developer toolbar for IE)
  http://www.microsoft.com/downloads/details.aspx?FamilyID=E59C3964-672D-4511-BB3E-2D5E1DB91038&displaylang=en
  
• Fiddler (a reverse HTTP proxy, inspect headers, view traffic)
  http://www.fiddlertool.com/
  
• Firebug (inspect and modify web pages, debug Javascript, view network stats)
  http://www.getfirebug.com/
  
• Firefox Live HTTP Headers (view HTTP headers)
  http://livehttpheaders.mozdev.org/
  
• Firefox Modify Headers (change your IP address, among other things)
  http://modifyheaders.mozdev.org/
  
• Firefox User Agent Switcher (change your browser user agent string)
  http://chrispederick.com/work/user-agent-switcher/
  
• Firefox Web Developer Toolbar (inspect and dynamically modify web pages)
  http://chrispederick.com/work/web-developer/
  
• .NET Reflector (inspect .NET assemblies)
  http://www.aisto.com/roeder/dotnet/
  
• .NET Resourcer (inspect and edit resource files)
  http://www.aisto.com/roeder/dotnet/
  
• Page Saver (save an entire web page as an image)
  http://pearlcrescent.com/products/pagesaver/
  
• SysInternals (Inspect everything Windows with Filemon, Regmon, PsTools)
  http://www.microsoft.com/technet/sysinternals/default.mspx
  
• The Regulator (edit and test regular expressions)
  http://regulator.sourceforge.net/
  
• WinMerge (compare and merge files and directories)
  http://winmerge.org/
  
• Wireshark (sniff traffic and inspect the lot across various protocols)
  http://www.wireshark.org
  
• YSlow (determine why web pages are slow to load)
  http://developer.yahoo.com/yslow/