My original prediction was the 18th. I figure I'll start labor the night of the 16th with the full moon and then she'll take a while to actually come out.
I say the 18th because DH and I were both born after 2 day long labors. Also, my MIL's birthday is the 16th and my mom's is the 20th, so the 18th is right in the middle of those.

(My EDD is the 14th, btw)