Ran across a CodePlex project today that seems to have some merit. Although it is in the early stages of development, ThoughtWorks’ (Martin Fowler, et. la.) project "White"looks promising and has received some good reviews. A few blurbs from their site explaining the product:

White supports all rich client applications, which are Win32, WinForm, WPF and SWT (java). It is .NET based and hence you wouldn't have use proprietary scripting language. You can use your favourite .NET language, IDE and tools for developing tests/automation programs.
White provides consistent object oriented API for all kinds of applications. Also it hides all the complexity of Microsoft's UIAutomation library and windows messages (on which it is based).

Third Party Controls
White works on top of UIAutomation framework of .Net. If you intend to or have third party controls in your application, you should verify whether they these controls are supported by UIA. You can use UIAutomationVerify http://www.codeplex.com/UIAutomationVerify to check this. When any controls is supported the tool would show you the inner details of the control in a tree form.

Silverlight Versions
White's released version doesn't support silverlight 3.0 yet, it support Silverlight 2.0. Although if you checkout the source code from trunk then it would work for Silverlight 3 as well.

64 Bit Windows
White is currently not tested on 64-bit windows, so you might face issues with it.

Would white support my application and controls inside it? (.....as I am not using standard .NET application)
White does support Win32, WPF, WinForm, SWT and Silverlight applications. In fact SWT is a type of Win32 application when running on windows. Powerbuilder, MFC, etc applications are all Win32 applications as well. In order to determine which controls are automatable, please use UISpy or UIAutomationVerify to check whether these controls are visible using MS UIAutomation. White is based on UIAutomation framework.