Some notes on monsters -- they are all original, in that there are no 'Jovian Orcs' or 'Space Dragons' running about. As for hauling things from the Monster Manual -- any vermin are good. Most of the humanoids will work fine if you change their skin colors a bit and give them genre-appropriate names. Mind flayers are great. Avoid obviously magical creatures, like elementals, unless you can make them products of lost science. Devils and demons and the like are pretty much Right Out -- too much fantasy baggage, IMO. Also avoid the 'classical' monsters -- gryphons, unicorns, and so on, unless you give them some good pseudo-sci-fi twist. Aberrations in general are good, especially if they are light on spell-like abilities. Umber hulks are good. Slimes and oozes are good. Anything which could reasonably be living in a large pit into which strange cultists hurl their terrified victims is good. And dinosaurs -- you can never go wrong with dinosaurs.