The SQLTeam Weblogs have been running for a few months now, with some great content. Of particular note is DavidM's series on DataTable Relational Operators in C#. David has written methods in C# to reproduce the relational operators Join, Union, Difference, Divide, Interect, Product, Restrict and TClose using DataTables. The series concludes with an example using the Northwind database.
If you are doing any work with DataTables in .NET this is a must read. Thanks David.