D-Class are primarily the FWD's
, so I'd love to see some Peugeot's, 106GTi, 205 GTi 1.9, 306 GTi-6, with the 205 and 106 getting engine upgrades to the GTi-6 and the GTi-6 getting an upgrade to the 406 V6. Though apparently Forza 4 only has the 206RC of note. The rest are crap, though the 1.8Turbo in the 207 is bloody awesome, pity about the car itself...
However I'm more a C class man so TVR's are my order of the day
Sagaris, Tamora, T350c and T440R, Speed 12 (first version) and Cerbera Speed 12 to round out the Veyron beaters
A Subaru 22B would suit me down to the ground though