Please, do not get a V6 Mustang. I bet my Focus could even keep up with one, especially if turns are involved.
I guess "top 3" in my book would be Civic, Eclipse (2 gens ago),or Integra. Not necessarily in that order. They all have a very strong aftermarket, and I'm sure you could find one in that price range. But anyway, please, please, do not rice it out. No huge wings on front wheel drive cars, that will actually ruin your handling. If you're going to spend money I saw an article in Sport Compact Car on how you can pick up used turbo parts and get an exhaust shop to bend some pipes for you, and have a turbo kit for $500 that will bring a Civic to over 200hp. Do that.
Power is nice and all, but I prefer handling. I never had much fun going in a straight line for a few seconds (probably because "a few" for me is 16 on the qtr. mile). And you also have to remember that power to a small car is not the same as power to a large car. For instance, I've seen turbo Focuses with relatively low (lower than V8) hp spank bigger V8 cars, just because of the huge weight difference.