The Nissan GTR is a good shout, would be on my shortlist. My mates got one running around 750bhp and the acceleration from a standing start is like nothing I've ever been in, there isn't much keeping up with it in a straight line. It's quite amazing how well it goes and puts the power down. You really need to have a good drive in one to see why they are so raved about.
How much are the Alfa 4Cs going for now? I'd be tempted to look at one of those for something a bit different and unique, don't see many about.