Italy: Smart
Not quite a supercar, but I bet chases on the narrow streets of Rome are much more interesting since the Italian Police got this.
USA: Dodge Magnum
Michigan Police acquired an entire Magnum fleet (they could be used as rams by their looks)
USA: Dodge Viper
Texas’ way of welcoming visitors
USA: Corvette C6
USA: Ford Mustang
USA: Hummer H2
700hp Hummer powered by a 7.0L supercharged V8 for a sheriff in Texas
UK: Lamborghini Gallardo
Similar to the Italian Police Gallardo, just with a crappy paint job
UK: Lotus Exige
The Exige is a lightweight, high performance car that accelerates from 0 to 60 faster than typical V8 cars and yet only uses around 5 liters / 100 km.
Australia: Holden VE Commodore