Are you looking at new or used, and a sedan or a coupe? What's your budget?

One of the fastest V6 coupes I can think of right away would be like a 350 or 370z. Theyre actually pretty well built cars but people typically rag the heck out of them.

There are some cars like the TRD Camry that have high output V6 in them, but its a FWD sedan, so the driving dynamics wont be as fun.  

You could also look at some American cars like the Camaro or Mustang, though the V8 is a good bit faster, their V6's still have a good bit of boogie and costs much less than the V8's. They arent the best built cars, but they arent total junk either. 

I'm from the states and dont know what your market is like, what cars & parts are easy to get and what's more difficult (and expensive) to obtain. 

Id also say if you open up to some turbo 4 cyls you then have more cars to look at, WRX, EVO, Civic type R.

Id recommend getting a manual, and if you are looking used make sure to have it looked over closely, these types of cars have probably been driven hard.  

Understand its hard to find something that's both fast & reliable, its a give & take. Id look at cars that you can get parts easily for so when things do eventually go you don't totally break the bank. 

Try out a Lexus GS350 F Sport that's a couple years old.  Available in rear wheel drive or all wheel drive.  Toyota has history of dependable V6 engines.