Considering the full list of PDC videos published here what are, in your opinion, the best session to download and see, considering their relevance to your work, technology and so on? Pleas, one session per answer (exception only for the sessions split in two parts) and please vote it so to move the best ones to the top.
I would have to say that my favorite session was the "future of C#" video, very nice to be able to see what is coming in the future for C# and the .NET framework.