Recommended Tools
Free
Dependency Walker
Dependency Walker is a free utility that scans any 32-bit or 64-bit Windows module (exe, dll, ocx, sys, etc.) and builds a hierarchical tree diagram of all dependent modules. For each module found, it lists all the functions that are exported by that module, and which of those functions are actually being called by other modules. Another view displays the minimum set of required files, along with detailed information about each file including a full path to the file, base address, version numbers, machine type, debug information, and more.
Dependency Walker is part of several Microsoft products, such as Visual Studio, Visual C++, Visual Basic, Windows 2000/XP/2003 support tools (on the Windows CD), Windows 98/NT/2000/XP/2003 Resource Kits, Platform SDK, Windows DDK, Windows SDK, and MSDN.
Commercial
HPS HwndSpy
HPS HwndSpy is a programming utility that allows developers to visually locate and inspect windows that are currently being displayed. When the cursor is moved over a window, HPS HwndSpy will display various attributes about the window, including its size, location, class, and style. This is very useful in analyzing windows in a deeply layered GUI application.HPS HwndSpy is an invaluable tool for developers doing maintenance on GUI applications, where they first need to understand the windows hierarchy and how the windows are structured. Unlike other tools such as Spy++, it is not necessary to use a "finder tool" with HPS HwndSpy. The HPS HwndSpy window properties view is updated automatically as the cursor is moved.

Highly recommended for anyone doing GUI work.
Axialis IconWorkshop
For a long time I was using another nice icon editor. Recently when I wanted to do some Vista compressed icons, I had to look for something else, because my icon editor doesn't support this.Fortunately Axialis IconWorkshop is even nicer and more powerful. Its ability to create stunning new icons using image objects is simply incredible.
When you buy IconWorkshop, you get access to free icon and image object packages (see here: http://www.axialis.com/objects/index.shtml). Cost: $69.95 for the Pro version
However, for just $79.95, you can get both IconWorkshop Pro and Cursor Workshop Pro in a bundled deal. See here for more info: http://www.axialis.com/promotions
Axialis also has a Free Upgrades For Life policy.