for the sassanids, shahreevar has set you covered pretty well. But just to call some names off the top of my head, Ctesphion (later Baghdad) was the capital. Susa, Istakhr (later Shiraz), Takht-e Soleyman, Hamadan, Nineveh, Derbent, Ardashir-Khwarrah (AKA Gor AKA Firouzabad), Balkh, Bishapur, Nishapur, Yazd, Rhages (AKA Reyy), Spahan (later Isfahan), Tauris (Later Tabriz), Antioch, Dezbar, Herat, Erebuni (AKA Yerevan), Ohrmazd-Ardashir (later Ahvaz), Merv and Nihawand.
EDIT: the first four cities were probably the most important ones after Ctesphion, and the rest are in no particular order.