I like the Cthulhu race
I also would love a Giger-like Biomechanoide race.
Or a race that is more... a thing, and doesnt look like a human in a 50's monster costume. Really, mostly i'm rather dissapointed by the design of the races. They all seem to have the same basic pattern. But, i'm not worried, for i know Paradox and i know, they will throw lots of good DLC at us, and we will surely be able to mod the hell out of this game.
So i just suggest a few more abstrakt lifeforms, like parasites, worms, virus or bacteria. Fungus is actually a great idea, but i dont think fungus should consist of individuals in spacesuits. They should really be more like an organism that grows on everything, travels via unsuspecting carriers, and spreads silently if not destroyed.
I also would like to see some transzendent species.