Is there any updated version of the SPSource reverse engineering tool for SharePoint or an alternative tool for SharePoint 2010?
Visual Studio 2010, preferrably with the Community Kit for SharePoint Developer Tools. This allows you to browse in the Server Explorer down to your list, content type or fields, and you can right click and 'import' them into your Visual Studio project. This then shows you the CAML used to define those items.
Another alternative is SharePoint manager - it also exposes the XML used to define those elements - but I find the Visual Studio tools more useful, 'cos generally I want to do something with those lists/content types.
Even without the Community Kit, you can still import List definitions with just Visual Studio, I think.