Im too lazy to read all of them so I am not sure if any of these has been posted yet:

Your mommas so poor she went to McDonalds to put a milkshake on lay away...

Your mommas so fat she got hit by a bus and she turned around and said "Who threw that rock?"

Your mommas so dumb I told her to buy me a color TV and she said "what color?"

Your mommas stink so bad, she made Right guard turn left and speed stick slow down...and even the secret told on her fat ass...

Ahhhh the classics.
And of course
Yo mommas so dirty she thought she was black until it rained.

Maybe tonight we'll fly so far away... We'll be lost before the dawn...