Its important to differentiate what Sergio Pininfarina collaborated on or guided, and what he designed outright himself. Pininfarina designs were more of a collaborative effort in the 70's and 80's; for example, the 308, 288GTO and Testarossa was mostly the work of the godlike Leonardo Fioravanti, the Enzo (and 996-shape Porsche 911) the work of Ken Okuyama. But that's like describing the difference between Bobby Moore and Sir Alf Ramsey; the man with the vision moulded the team in his image to drive the team towards the ultimate goal.
But having said that, here's one that is totally Sergio Pininfarina, and if he had never picked up a pen ever again after styling this, his legend would still have been complete:
The Ferrari 250 GT SWB.
From here, this particular car came up for auction at Pebble Beach in 2010.
The legendary 1961 Ferrari 250 GT SWB Berlinetta SEFAC Hot Rod
The 250 GT SWB Berlinetta was the ultimate Ferrari GT for years since its 1950s prototype debuted, with a shape so pure and well balanced that Sergio Pininfarina called it "the first of our three quantum leaps in design with Ferrari." One of only 20 cars built, this SEFAC (Scuderia Enzo Ferrari Auto Corse) chassis 2845, was sold new to Count Volpi under the manager's infamous Scuderia Serenissima (Volpi's own racing team). It has an extraordinary racing history that includes a very impressive Third Place at the Tour de France, finishes at the 1000 Km de Paris and Daytona 3-hour Continental as well as multiple Italian hill climbs and vintage races throughout Germany.