I have read the Threading in C# tutorial written by Joseph Albahari.
It is by far the most complete, yet easy to read tutorial I have read so far on threading in .Net. It can also serve as introductory material for anyone unexperienced with multi-threading concepts. Most .Net / C# books usually have a chapter or two on the topic but most often just scratch the surface of multi-threading in .Net.
I highly recommend anyone to read his paper.