Webpart Connections from MSDN library

Really interesting article : building connectable webparts

Smart Part 1.0 interesting features for ICellProviderUserControl and ICellConsumerUserControl  : http://weblogs.asp.net/jan/archive/2004/11/23/268644.aspx

SmartPart connectable demo from author : http://weblogs.asp.net/jan/archive/2005/12/01/432020.aspx

Behind the smartpart, something like that : http://www.codeproject.com/aspnet/LoadingUSerControl.asp