There are 113 domain models over at eclipse.org site of all sorts of things.  I guess most models don't have any practical value (what will I do with a metamodel of COBOL) but there are several interesting ones of things like RSS, WSDL, and SDM

It is also interesting to note that the models are expressed in several forms including MS DSL models  , UML 

  and images . The transformation from format to format was done by code.

(Found via Steve Cook )