Looks to me like the Mitsubishi Evo VI is a photo taken somewhere in Britain*...but I've certainly never seen an Evo VI police car - the newer cars are generally Volvos and Range Rovers
The XJ220 looks like it says "Grampian Police" on the side which is again british, and the number plate looks just like english ones do, so that must've been taken in England too...but I'd say the chances of ever seeing that on the road here are seriously slim!
[just noticed steering wheel on the right, as well]
I heard one of the police forces here bought a few Porche 928s for high speed work, but again, never seen them or heard anything more.
At a guess, I'd say the A-class is in Spain (or perhaps Italy)...my Spanish is very poor, but I think POLICIA is spanish - correct me if I'm wrong!
And just my opinion on cars in general - I'm looking forward to getting a Volkswagen (or Audi) Turbo Diesel when I've got the money to afford it. I can't say that I have any experience of American cars beyond being in one or perhaps 3 occasions, but the Germans really have got a good thing going with their cars - I can't imagine anyone being better at the end of the day!
*the hint is the way that it's rained recently
...oh, and the colour scheme is just right with the reflective paint down the side...