DebugView: An indispensable utility from SysInternals. I use it as a UI for BizTalk—by printing debug information using System.Diagnostics.Debug with its default trace listener, messages end up getting fed into the Win32 OutputDebugString function. DebugView monitors and displays this debug output.
TCPTrace: Tunnels packets between a client and server, and displays the payload. Unreal for tracing HTTP traffic between web services, WCF endpoints, etc.
XPathMania: Extends the VS.NET 2005 XML Editor, by providing a “scratch pad” to enter and execute XPath queries against the active document.
LoadGen: Microsoft’s free load generation tool, supports a variety of protocols out of the box. It is built on an extensible (configuration based) design (presentation, framework + component), and is open to customisation.
adminpak.msi: The windows server administration tools pack provides a bundle of useful tools for working within a distrubuted Micirosoft environment. I use the MMC remote desktop snap-in and active directory administrative tools daily.
WinMerge: An incredible open source diff/merge tool. New version of an old schema, and want to see the differences? Branched an orchestration (odx) and need to merge the changes back into the trunk?
SQL Server Profiler: This handy tool gives visibility to the TSQL statements that are submitted to a SQL Server. It can be run remotely from the SQL Server itself. Its an install option that is included with the standard SQL Server Client Tools. Last time I used it was to diagnose a heavy map that had way too many custom scripting functoids—many of which were doing data access lookups.
Foxit Reader: This one has nothing really to do with BizTalk or development… it is however the fastest, lightest PDF viewer I have ever come across. Its speed is just incredible.
“Scott Hanselman’s 2007 Ultimate Developer and Power Users Tool List for Windows” is the best tool list I have come across. Many life changing, productivity tools for a developer.