Dino Esposito's ASP.NET control development articles on MSDN
A Crash Course on ASP.NET Control Development: Building New Controls from the Ground Up
http://msdn.microsoft.com/asp.net/default.aspx?pull=/library/en-us/dnaspp/html/ContCrshCrsNew.asp
A Crash Course on ASP.NET Control Development: Building Data-Bound Controls
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/ContCrshCrsDB.asp
A Crash Course on ASP.NET Control Development: Deriving New Controls from Existing Classes
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/controlscrashcourse-deriving.asp