VocalSynth Pro is very nice for science fiction voices, and Vocal Doubler is good!
I make old-time science fiction radio plays and do all the voices--except the female voices, which I do with Realivox Blue (RealiTone), my favorite virtual female soprano (runs in Kontakt and is controlled with music notation and phonetic scripting).
VocalSynth Pro is excellent for science fiction voices, robotic voices, and other outer space types of vocal tones and textures.
I like Vocal Doubler, too.