I was playing with the SHAutoComplete API call and the IAutoComplete (2) interface last night (adding auto-complete to an application of mine) and I found a neat article and related component on CodeProject...

C# does Shell, Part 4 by Arik Poznanski

This article is about the AutoComplete features provided by Windows and how to use them with C#. AutoComplete is the ability to expand strings entered into an edit box. The article will develop a class for using this functionality in your applications.