I was at a party last night as a pirate. I had been a lion tamer, but as we found a last minute sitter for ds, it didn't really make sense w/o his little lion but.
so, pirate was easy: sexy bustier, all the rings I own, tight pants tucked into knee boots, big hoop earrings, pearl necklace, bangles & baubles, striped scarf around the waist, daggar, scarf around head, & pirate hat.
Now, I have all these things, but you could easily tailor it to what you have.

: My girlfriend was examining me at the party and, this is a direct quote, "Dag! Are those just regular clothes?"

: Yep, but I looked hot!
Now, I'm the type of person that keeps a bag of dress up stuff around, so I may not be the best to ask...and it depends on what you have and how your humor is...
Last year dh & I (7 mos pgs) went as Brittney & K-Fed, I wore a naughty school girl outfit & blond pigtails and carried a baby doll I kept dropping. DH got all g'd out and I bought him a fake spinner necklace & a giant fake magnetic diamond earring. He tied on bandana a'la Tupac, wore a jaunty trucker hat, and a knee brace and all night referred to himself in the third person ("K-Fed needs another beer!") and talking about his super-sweet secret dance move he was perfecting.

Oh, we won a prize for that one!
Anywho, maybe you could go as the valedictorian if you have a robe...last night dh went as the elephant man, which entailed cutting an eye hole in a pillowcase. (he always wins least effort) One year he went as a bloody tampon and drew red magic marker on a white shirt and a rope out the back of his pants (he has red hair, so that helps). As I type this, if pregnant nun got burned, I'm sure bloody tampon is going to start a hell storm!

Oh, well, we have warped senses of humor.

To each his or her own.