UPDATE 4/12/2012: I just noticed the links below are dead.  You can still find the webcasts on MSDN though: http://msdn.microsoft.com/en-us/exchange/aa731550.

I keep recommending these webcasts to people individually so I figured I should mention them here.  The EWS team put together a series of six webcasts on called “Exchange 2010 Development” but it really focuses on Exchange Web Services specifically.  If you are looking for information on Transport Agents or Powershell there’s not much here unfortunately.  However, they go into great detail on essential EWS knowledge.  If you are doing any EWS development this series is a must watch.