Some good choices here.
250GT definately in and the Speedster has to stay if only because of its association to James Dean.
Murchialago - As much as this is my current favourite car, cool??? im not so sure, I think flash is probably a better description.
F355 Challenge - An undoubtable drivers car. However, the fact you'd have to explain that its a challenge model would probably make it uncool if we were to use Clarksons rule of thumb.
F40 is a tough one, probably the ultimate 80's supercar, but would non-car people appreciate the lack of carpets, the pull cord for a door handle and the fact that the paint is so thin that you can see the bodywork through it (all this impresses me, but to a non car nut?????)
Countach - Undoubtable the best looking supercar throught the 70's and 80's and lets face it Cannonball Run wouldn't have been the same without it - but when I think of it now, all I see is DelRoy from 80's band Five Star standing next to his outside his mock tudor house in Romford - sorry uncool!!!(unless you are a Five Star fan)
VW Camper - Uber cool but only in the VW Scene, not exactly the car to drive around casino square in!
288 GTO - Ok I know Magnum had a 308, but if I had this I'd feel i'd need to grow a moustache and unfirtunately I can't
Veyron - magnificient - but cool???? (again if you had a DB5 in your garage and a Veyron, which one would you use to go to Monte Carlo in??
Audi UR Quattro - Only cool if doing the monte carlo rally, but once i'd won that I'd want to arrive at the after party in my Gullwing lol.
Just my opinions guys