Whatever car you like, if you like what your driving it will boost your confidence and thats what matters. Some say cars attract girls, thats true but not directly... when you are proud of your ride it shows. If you park your car, walk into the place and your still feelin like "the man" just b/c you know that car is waiting for you outside, that's the right car. Personally Id say:
For the older and/or more mature guys: Any high-end luxury car, or high-end performance car.
For the younger and/or more "rebel" type: Any loud muscle car, possibly an import but personally I think the loud muscle cars are SO much more intimidating, which adds to the whole "rebel" image that the younger girls seem to love.
either way, convertible is a plus. I have an 02 Mustang GT, sonic blue, chrome rims, LOUD.... get nothing but compliments.