The Nissan Skyline R32 ran in the Australian Touring Car Championship in the early 1990s (http://www.youtube.com/watch?v=uh5cRc3fxRo).
A couple of models of Audi Quattros ran in TransAm and IMSA in the late 1980s (http://www.youtube.com/watch?v=X53Yxp2QTU4).
The Audi A4 (as already mentioned) ran in AWD for some seasons in a few of the European touring car championships.
Audi 90 Quattro IMSA/GTO, Opel Calibra DTM, Super GT Subaru Impreza, the Nissan Skylines that ran in the Australian Supercar championship, can't remember more atm
There's the Mercedes CLK AMG DTM and the Opel Astra OPC DTM wich are both road legal... they are having something like 350bph using a bodywork wich looks similar to the DTM's body work and are quier Porsche-Killers on the road. But those where only produced when the new DTM was getting known here in Germany... However one of the Sheikh bought one of the Mercedes DTM cars along with a Mercedes CLK LeMans and built himself a private road to drive them
To be serious I don't know about it I hardly remember anything about the old DTM, cause I was too young, and though I am interested in the old DTM's races nowadays, I don't care about the cars.