BABES WITH BLASTERS, Experimental Babes, Alien Babes, and more -- all at Babes in Space, a collection of lurid cover art from science fiction's pulp era.
UPDATE: There's a massive collection of space babes here, arranged by decade, from movies and TV. And TexasBestGrok has a poll running for "best SF babes" from Dr. Who. Here's a gallery of previous winners.
It's amazing the links people will email you once you post on a subject.