If you want something you can modify, I will the suggest the 5.0 too. There is just an insane amount of performance parts for it. The 5.0 is probably cheaper and more fulfilling to modify than something like the Talon/Eclipse.
I will also suggest the GTI 1.8T if you don't mind a small car. The 1.8T has lots of potential and a lot of performance parts to play with. Though, it's not as sporty looking as the 3 cars on the list... it's a box on wheels, you know.
