I was recently made aware of a tool which should absolutely be a part of every WinForms developer’s toolset, Managed Spy:

Similar to how Spy++ displays Win32® information such as window classes, styles, and messages, ManagedSpy displays managed controls, properties, and events. ManagedSpyLib allows you to programmatically access Windows® Forms controls in another process. You can get and set properties and sync on events in your own code. ManagedSpyLib can also help you build test harnesses and can perform window, message, and event logging.

A few interesting points to note: first, the tool is factored into ManagedSpy, an application that helps you debug your WinForms applications, and ManagedSpyLib, the underlying library (used by the ManagedSpy app), which provides programmatic access to running WinForms apps in another process via a mechanism called a ControlProxy. Second, the full source is included, so you can not only use it, you can learn from it, and customize it. Last, note that it only works with .NET 2.0