I was perusing my D&D 3E Monster Manual today and I noticed that several of the monsters in it would make excellent aliens.
They break down into three main types, here are some for a start:
Non/Semi Intelligent Alien Wildlife
Ankheg - great for bug hunts!
Assassin Vine - watch where you're stepping.
Behir - dumb them down a bit and they'd make great aliens for an ice planet.
Bulette - one of these landsharks could really ruin your day (and ATV).
Carrion Crawler - just nasty.
Darkmantle - nasty cave dwellers, make their Darkness ability psionic.
Digester - get an acidic surprise from these otherwise normal dinosaurs.
Dire Animals - great everywhere (Ancients' manipulations again, or Solomani experiments?).
Frost Worm - again great for cold worlds - treat their Cold ability as a kind of super-heatsink that makes them impossible to detect on infrared.
Krenshar - alien great cat replacement.
Oozes - fantastic trappers.
Intelligent Aliens
Aboleth - just treat ALL of its abilities as psionics, of a particularly alien kind.
Dopplegangers - obviously psionic aliens with that classic sci-fi ability to mimic a target's appearance (alien spy creature got loose?).
Mind Flayers - evil psionic predators, even the Zhodani are afraid of these guys.
Possible PC Aliens
Formians - play an insect!
Gnolls - Vargr's ugly cousins?
Goblins, Orcs, Kobolds, etc. - good barbarian cannon fodder.
Grimlocks - interesting alien race.
Kua-Toa - nasty frogmen.
Lizardfolk - just give them FGMP-14's and let them go for it!
Locathah - nasty fishmen.
Lots more ideas in there ... what are yours?
They break down into three main types, here are some for a start:
Non/Semi Intelligent Alien Wildlife
Ankheg - great for bug hunts!
Assassin Vine - watch where you're stepping.
Behir - dumb them down a bit and they'd make great aliens for an ice planet.
Bulette - one of these landsharks could really ruin your day (and ATV).
Carrion Crawler - just nasty.
Darkmantle - nasty cave dwellers, make their Darkness ability psionic.
Digester - get an acidic surprise from these otherwise normal dinosaurs.
Dire Animals - great everywhere (Ancients' manipulations again, or Solomani experiments?).
Frost Worm - again great for cold worlds - treat their Cold ability as a kind of super-heatsink that makes them impossible to detect on infrared.
Krenshar - alien great cat replacement.
Oozes - fantastic trappers.
Intelligent Aliens
Aboleth - just treat ALL of its abilities as psionics, of a particularly alien kind.
Dopplegangers - obviously psionic aliens with that classic sci-fi ability to mimic a target's appearance (alien spy creature got loose?).
Mind Flayers - evil psionic predators, even the Zhodani are afraid of these guys.
Possible PC Aliens
Formians - play an insect!
Gnolls - Vargr's ugly cousins?
Goblins, Orcs, Kobolds, etc. - good barbarian cannon fodder.
Grimlocks - interesting alien race.
Kua-Toa - nasty frogmen.
Lizardfolk - just give them FGMP-14's and let them go for it!
Locathah - nasty fishmen.
Lots more ideas in there ... what are yours?