I thought it would be good to create this Wiki listing out and possibly linking to all the different car genres and modifications and groups.

Starting out:

Classics (era?)	Link
Drifting	Link
Kit Cars	Link
Military Vehicles	Link
Luxury Barges	Link
Rat Look	Link
DTM	Link
Japanese Imports	Link
'Flushed'	Link
4x4	Link
Off Roaders	Link

Please add to this list... and possible add any interesting links.