Everyone is familiar with this functionality. If you open up the the outlook address book and start typing a name, the list below the searchbox instantly filters to only contain items that match your query. .NET Reflector has a similar feature when you're browsing types ... you start typing, and regardless of how large the underlying assembly is that you're browsing, it's near instantaneous.
I've always kind of wondered what the secret sauce was here. How is it so fast? I imagine there are also different algorithms if the data is present in-memory, or if they need to be fetched from some external source (ie. DB, searching some file, etc.).
I'm not sure if this would be relevant, but if there are resources out there, I'm particularly interested how one might do this with WinForms ... but if you know of general resources, I'm interested in those as well :-)