Threads like this pop-up pretty frequently on Pistonheads. Opinions and rationale of what makes for a cool car seem pretty diverse - but that's what makes reading the threads fun.
For what it's worth, my (totally subjective) "criteria" for a cool car would be something along these lines (I'm ignoring the argument that by simply deeming a car cool means it no longer is!):
• Beautiful with classic proportions - many modern cars have become bloated (largely to correspond with safety regulations) and incorporate different aero devices, things which detract from the overall aesthetic.
• It shouldn't try too hard but instead needs to have an effortless quality, not scream "look at me, look at me!" – many modern sports and super cars, whilst being brilliant from an engineering perspective, fall at this hurdle.
• It has to be useable in a day-to-day environment - it isn't cool to go around stressing about speed bumps and whether it's going to rain or not. It also helps if it has at least a cursory element of practicality to it.
• Whilst a car should primarily be bought because you alone want it, it's a nice by-product if members of the opposite sex are drawn to it! To those ends, it's desirable if the right kind of member of the opposite sex is drawn to it, i.e. not money-hungry wag-types who make a b-line for any given Ferrari, Porsche etc. no matter how bland. It should appeal to women with a more refined appreciation of style and taste.
• Its appeal should not have to be explained, it should speak for itself. Therefore, if you have to explain "Oh it was the first to have this..." or "It was the first to win this..." to make the car interesting, it's not cool.
• It shouldn't be too common a sight on the roads.
• Just because Steve McQueen etc. once drove something similar doesn't mean it's still cool when being driven by a "chubby, balding fifty-something guy working in finance". Just because a car works for one person doesn't mean it will for someone else. It has to match your own sensibility and personality and you have to be comfortable owning and using it.
So, after all that waffle, what would I pick?! Well, certainly a nice Citroen DS or a Lamborghini Miura SV would meet the above. However, as these have already been mentioned a few times (plus I’m pretty sure I’m too tall for a Miura!), I think either of these would do nicely…
Ferrari 275 GTB 4 (in red or dark blue) (took basic lines from the 250 GTO, but looks a little more elegant)
Maserati Quattroporte Sport GTS (in black)