The Rebel Blockade Runner is the very first ship we ever see on screen in Star Wars. I always felt it was modelled after a Hammerhead shark. The folks at ILM added a micro Star Wars poster and Playboy centerfold within the cockpit of this ship that is not visible in this image, although does appear on the packaging one of Kenner's recent toys.
The detail on the engines gives a "worn" look, as if the engines have been in use for a long time. This style is fairly common among the Star Wars vehicles, particularly the Rebel ships.
In Return of the Jedi, the Calamari introduced some large ships into the Rebel Fleet, or so the story goes. At the San Francisco exhibit, there were two different Calamari cruisers.
Here's a shot of that same ship from the side. It almost looks like a Gaudi building.
This Calamari vessel has little wings on the side, but overall has the same look and feel as the other Mon Calamari ship.