The brainiest non-mammalians--birds, cuttlefish, octopi--strike me as offering good clues for what a brainy extraterrestrial might be like. Rather than big-eyed little humanoids (E.T.; Close Encounters) or large and athletic humanoids (Avatar; Predator), my bet is that a resemblance to the serene countenance of a cuttlefish, or the hyper-alert face of the pictured crow, is more likely. That's assuming these hypothetical aliens have a face at all, of course--while radial symmetry is a viable option, it suggests to me a grazer or a filter feeder, which wouldn't likely gain much of an adaptive advantage in developing a big brain.

But then elephants are grazers, so a diet of low nutritive value certainly can sustain intelligent creatures with rich social lives. And baleen whales are filter feeders, and they are intelligent and touchingly social creatures, too.