Assuming 2.0 as a starting point, 3.0 added the first WPF, WCF and WF bits.
3.5 further extended the offering and added AJAX bits as a native part of
the framework, as well as some Silverlight bits (the 1.0 version). 3.5 also
integrates AJAX and WCF and adds more interoperability to services.
Here is one page (3.5):
http://msdn2.microsoft.com/en-us/library/bb332048.aspx