This is very difficult. I can't really keep it to 5 and I can't really decide on the order.
My dream car to have for a race car is an Opel Vectra Super Touring car, so this would have to be near the top.
The Opel Omega EVO500 has always been a bit of an enigma to me. It isn't a particularly great car in road going form, and is far surpassed in performance by the Lotus Omega/Carlton, but the EVO500 just looks so great and I love NA engines.
The Kadett C was close to my heart after I got my first Chevette (I never quite grew to the front on the Chevette) and the coupe in GTE form is particularly nice.
I'll put these two on the same level. The Ascona B was the first one I decided I wanted, particularly the 400, however I love the shape of the Commodore B coupe that it would almost win favour if I got an option of either.
I think the 400 would be a little more exciting than the Commodore though!
Others? I love some of the other DTM cars, though I never really had the option to follow it much being that it has never aired in this country.
The high rpm screamer Calibra.
And the Opel Vectra C
Obviously my bias is a little towards the race cars, but I really like a lot of the road cars, just many are not particularly exciting in their standard form.
Great thread, looking forward to some of the other cars and I'll probably change my mind on a few by tomorrow.