512 BB - Fun but a can be a handful like other have said. I knocked out a few races with this but eventually upgraded to a 458 for my Ferrari/Italian car. The 458 is a monster! Very fun and very fast! With some tuning, you can use the 458 all the way through the GT "Word Championship".
Also used a '06 S2000 for several races. Tuned to 320 hp with some weight reduction it was pretty quick, but prone to oversteer, although not as bad as the 512 BB.
Corvette ZR1 is a bargain at around 100K.
Not a fan of the Gallardo. It did not seem nearly as quick as the 458 and was harder to keep in control. Since it is a 4WD car, the handling characteristics surprised me a bit.