What is more terriffying than huge monsters? Dragons make even experienced party nervous and humongous monsters are something 21th century people are not used to. It doesn't matter how big your laser weapon is if your opponent's is bigger and it's armor thicker. Here are the monsters, that make your player's characters weep.
Disclaimer: I found this neat picture somewhere around internet. Unfortunately I don't know the source for image compilation nor who the original artists are.
So, I apologise for violating copyrights, but these pictures are so awesome. So, who ever you are mr. or mrs. artists, thank you for inpsiration!