The unknown DGEX, and this picture may make it famous.

It's not really unknown- it's just been pushed aside by the DGIV and XR series.
The big problems with DGEX are that it's never developed, it has a dearth of documentation, and it takes forever to get to orbit.
It is very nice however- some texture improvements, interior modeling, finishing the systems (Plasma Engines!), and working out the bugs, and it will be right up there with XR1. I very much like the concept of a more fleshed-out, muscular DG.