The Enzo is the fastest production, street-legal Ferrari. I am assuming you were asking about Ferrari cars since it is in this section but correct me if I am wrong. If you were asking about the fastest production car in the world then it is officially SSC Ultimate Aero because they claim among other things that they will build 25 cars (the minimum requirement for production homologation). In my opinion, until they build the required number, the fastest production car is still the Veyron because it is a true production car with over 125 already delivered, more than 200 orders still to be satisfied, and Volkswagen has even announced ramping up production meaning that they are committed to the project. Until SSC delivers more than 25 cars, it is just another promise like the Vector M12 which was supposed to be a "production" car and arguably 14 units were produced..
thats entierley debatable now... the new 430 challange stradale is faster around the test track and nurimburg ring than the enzo... The fact is that the enzo is a old car now and its technology is trumped by the current ferrari tech... i wouldnt be suprised at all to see the 430 challange stradale and the 599GTB pull a full second per min and a half of track on it through the road course... in a straight line im sure it would still be the fastest... as far as fastest car goes... im gonna be different and say that the Ascari A10 is probabally the fastest street legal car in the world as far as track times go but im hoping for the new Corvette ZR1 to be the new king... It is the fastest STreet legal car around the Ring but the Enzo, Ascari A10, and Bugatti Veyron (along with other top guns) have never been officially Power lapped around the nurimburg ring... and id take the vette anyways because i can afford somewhere to keep it too with all the money i saved !!!!