Floro Dery was the design supervisor for the original Transformers cartoon, back in the 1980s, and he's selling some of his art as signed prints on Etsy. And it's just absolutely beautiful. Check out this concept art for the "Mechano-beast." And below, there's a great illustration of Cybertron — and its robot mode.
This concept art for Cybertron and its robot mode was already sold on Etsy, but you can still buy the above print of Mechano-beast. And the one below the Cybertron print, showing the Crystal of Power, is also still available. [Etsy via Seibertron]