While I don’t have a comprehensive list, I do want to point out these four changes in particular because these classes are fundamental to the API.  If you have written code with the Beta 2 client API, here are the changes you will need to be aware of to use the RC client API.

• TeamFoundationServerBase is now TfsConnection.
• TeamFoundationApplicationInstance is now TfsConfigurationServer.
• TfsTeamProjectCollection replaces TeamFoundationServer.
• TeamFoundationServer is now obsolete.  It still works, but there are limitations with using it because it is not aware of collections.

[UPDATE 2/12/10]  Jim Lamb has posted updated TFS SDK docs: http://code.msdn.microsoft.com/Project/Download/FileDownload.aspx?ProjectName=TfsSdk&DownloadId=9107.