All "Alfa-Nord" (transaxle) have been produced at Arese. As long as Alfa kept being independent, 4-in-line and V6 engined cars were rolling out of Arese and flat-4 engined ones (Alfasud, Alfasud Sprint, 33) were made in Pomigliano, with the sorry exception of the ARNA produced at Pratola Serra, provincia di Avellino.
Spiders were also assembled, from a certain point, by Pininfarina in Turin. Not sure from which year.
After Fiat's buyout, it became more complicated as Fiats, Lancias and Alfas were built on the same lines. Yet the 75 (Milano) line remained at Arese up to the end. 164s were also assembled in Arese together with Themas. I seem to remember that the GTV/Spider (916) was the last complete Alfa assembled at Arese (not up to the end of production as at some point it's again Pininfarina who followed assembling them), then the plant only produced the V6 engines. The very last cars built at Arese, about 3-4 years ago, was the Fiat Multipla running on methan gas. Now it's virtually closed as there are only offices left and a small experimental department.
Arese was inaugurated in 1963 and the first car built there was the Giulia GT. Then the Giulia sedan production was moved from Portello to Arese. But the production of machanical parts went on at Portello for many years after that.