Hot hatches are great - for that money I think the Fiesta ST is the best one available. I've driven one and it really won't disappoint you as it's quick, nimble and economical too.
Alternatively you could get something a bit bigger and older - maybe a BMW 3 series or something similar (you can get an old M3 or even M5 for that money but they're very expensive to run as they guzzle fuel)?
Another option is a sports car, something like an MX5, s2000, or MR2 is an option or you could go crazier and get a lotus elise, Vauxhall VX220 or even a TVR Chimera (thought the insurance and fuel might kill you on the latter and they aren't reliable).
Final option is a classic car - an old rover, Jaguar or sports car like an MG or Lotus Elan or similar there are really so many options. Look through Autotrader at all the interesting options with your price limit set and you'll be astonished you can get some very interesting cars for that money if you look in the right place!