The ultimate little grey plastic promo plane is this TWA Jetstream (officially the Lockheed Model 1649 Starliner) from 1958. This is one of the most graceful of all with its long wings and long range, but it arrived too late and was already outdated. The first 707s were right around the corner and they became the new glamour girls.
TWA didn't miss a trick in its promotion. The name "Jetstream" is emblazoned on the wing, allowing even the most seasoned traveller to believe he was flying in a jet plane.