Space monsters have been suggested quite often; search the forums for "monster". Here's one thread dedicated to them, which has links to earlier discussions:
http://www.shrapnelgames.com/ubb/For...ML/001442.html
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Cap'n Q
The most merciful thing in the world, I think, is the inability of the
human mind to correlate all of its contents. We live on a placid
island of ignorance in the midst of black seas of infinity, and it was
not meant that we should go far. -- HP Lovecraft, "The Call of Cthulhu"