GTI = nice car, overpriced, a B word on repairs.
Civic Si = I don't consider the Honda Civic a sports car. I have the DX because it cost me nothing. The SI will cost you more on insurance and probably break down more often because you will beat it up since it is a sportier car.
Eclipse = Uh, it's nice but it's American. I don't trust American sports cars unless they are the Corvette or the Viper. Kind of a class above the other cars you mentioned though.
Mazda 3 = I love it. My sister bought one and I wish it had been me. For an inexpensive car, it's fun to drive.
Camry = Family car
Scion = Know nothing about it.
That's the problem. Sportyness costs money. Personally, I think I'm going to keep my Civic till it dies, which at the current mileage is in a very long time, and go pick up a second used sports car or SUV. Something that I would drive just to go out or on different occasions.