^ Sure there's a place for monsters in Traveller; some of my favorite NPC's are monsters in their own right!
I worked with another thread-head a while back on a list of space creatures that were treated like gods by some cultures and as monsters by others; here's the list:
Zadgaag - the god who grants/inflicts psionic powers - actually the Zadgaag are a mysterious race (like the Vorlon), secretively abducting and implanting sentients with psi organs/DNA. Their motivation appears neither benevolent or malevolent, just curious, but their plans are more complex and convoluted than can be imagined.
Kuragan - the god who owns/guards jumpspace - the Kuragan are like void kraken; semi-intelligent and highly aggressive energy beasts that wander J-space, attracted to the distortion made by charged lanthanum like a fish to a sparkling lure.
Eshkaseri - star spirits - the Eshkaseri are plasma based life forms that inhabit in the corona of stars. They are able to travel interstellar distances on the crest of large solar flares. Occassionally, when they come into contact with electronic and electrical equipment they are able to manipulate, the result is haunting voices echoing from speakers and curiously organized data logged into memory cores and other devices.
Lagkhidka - spirits who live in gas giants - the Lagkhidka are great balloon beasts that ride the thermals in gas giants like kilometer wide jellyfish. They are semi-intelligent and communicate by electrical discharge and radio waves. Their feathered tentacles fan swarms of airborne plankton into their cavernous maws. They are preyed upon by fast moving winged creatures that propel themselves with organic chemical jets. Their only defense is massive electrical shocks delivered through their tentacles. How they have become so wide spread in this quadrant is a mystery. (Thank you Carl Sagan).
Sashzugga - spirits who live in the Oort clouds - the Sashzugga are giant ice worms, boring massive passages through cometary bodies in search of complex hydrocarbons; their metabolism so slow that they barely radiate heat greater than their surrounding ice. They are able to elongate and flatten their bodies to form crude solar sails to travel between stars. Occassionally, one is drawn into the inner system of a star on a rogue comet where it absorbs enough energy to fission into millions of gosamer offspring who ride the solar winds back out into the dark.
Sugla - spirits who live in the Rifts - the Sugla are dark matter creatures the size of moons, yet only detectable by their gravitational influence and complex magnetic fields. These strange creatures only consume the sub-atomic particles evaporating off mini-black holes left over from the Big Bang. They hide in the great expanses between the galactic arms, as interaction with all other matter appears to cause a violent reaction.
Dapaaraag - the god of systems (and order) - Dapaaraag is actually an ancient machine intelligence whose nodes are spread out across interstellar space in apparent randomness. It is so devoted to its complex calculations that it seldom interacts with other lifeforms unless tempted with rare data. Even then, its responses to questions may take years to come and then be unintelligible without an understanding of high order mathematical theories and concepts.
Gushiig - the god of chaos (and antimatter) - the Gushiig are apparently homicidally insane creatures from an alternate anti-matter universe, trapped in this one with no means to go home. Driven by fear of total annihilation and with thought only to their own survival, they aggressively eliminate any normal matter that comes within range of their gigantic space-going fortress. The Gushiig learned sometime after their arrival to harness M/AM reactions to drive their monsterous vessel and power their equally frightening weapons. It is suspected that individual Gushiig are routinely sacrificed to power their dreaded machines. The Gushiig are being drawn to the galactic poles and the streams of anti-matter rushing from the core. They hope some may have coalesced into a planetary body they could inhabit. As is their murderous way, they will destroy anything that stands in their path including stars and planets.