I spend quite a bit of time each week in Mayfair, London (our office is next door to the US Embassy in Grosvenor Square)...and although I don't always have the time to get pictures, I see a lot of cool/expensive stuff.
Most impressive was probably a gold-plated (not painted - google it for some images) Bugatti Veyron parked outside the Dorchester Hotel, but in some place Lambo's and Ferrari's are quite common. The highlight, if you can call it that, is now being called the Arab Summer, because the rich young Arabs come to stay in their London residences during their summer, but have their cars shipped over for them - hence the gold plated Veyron.
There is a also a specialist car dealer - Bob Forstner - on Park Lane which deals with Brabus cars and often has things like a Mercedes 300SL, DeLorean and so on in the window - earlier this week there was a James Dean style Porsche in the window.
I'll try and get some pictures as I go around.