EasyHook - The reinvention of Windows API Hooking
Valgrind - Valgrind is an instrumentation framework for building dynamic analysis tools.
madCodeHook - "madCodeHook" offers everything you need to hook code (mostly APIs).
WinAPIOverride - WinAPIOverride : This software allows you to monitor and/or modify any function of a process for any calling convention (stdcall or cdecl)
Microsoft Research Detours - Detours is a software package for re-routing Win32 APIs underneath applications.
Process Monitor - Monitor file system, Registry, process, thread and DLL activity in real-time.