Well a few things to consider,

An Audi S4, buy a used one a few years old. If you live in Sydney I can hook you up with a friend who owns a euro garage. Does awesome mods on the Audi's. Currently has an S4 with 500 horse power. So its very fast.

AMG (Merc's) are releasing new mods from what i've heard and they're supposed to be very slick and make the new Merc's super fast. So I guess if you get the merk, the SL is pretty nice. You could try to look into the new AMG mods? Though I would say they'd cost you as much as the car lol

I really recommend the Golf GTI (R32 if you want top of the line) But my sister has one, and it runs with 300 horse power atm and it is amazing to drive. Smooth, powerful. And with a little bit of modding, you turn a lot of heads with it. Hers isn't the new model its i think the '04 or '05 or something kicks the shit out of any skylines really. Or maybe they just can't drive.

The Mazda 323 MPS is amazing. its the fastest stock small car on the market atm that we can get our hands on for a good price. Another good car is the Focus XR5. Both of these range between 30 - 45 k. So it'll leave you plenty of money to do some mods to it. I would recommend getting some XENON HID's or even Angel Eyes if you want to be different. Nice exhaust, new chip (supposedly theres a new chip out for the XR5 that can give up to 80KW) and some nice rims to compliment it al with.

The car that i'd choose from anything would probably be the R32, or the MPS. I really like the XR5 too. Hard to choose just one dammit! Haha.