Visual Studio (IDE)
WPA (performance analyzer)
WinDbg (debugger)
IDA Pro (disassembler)
dotPeek (decompiler for .NET)
WinMerge (diff tool)
HxD or 010 editor (hex editor)
Speedcrunch (calculator)
Firefox (browser)
Rohitab API monitor (API call monitoring)
SOS (a WinDbg extension for .NET)...