I just saw this race on Living Social today:
It's an adventure race and involves solving clues and knowing your way around DC, but if you win you get $750! Here's the website. If you sign up today via Living Social you can register for $35 instead of $70.
My experience with these types of races is that competitive runners can DOMINATE with a little planning ahead. I, unfortunately, won't be able to participate :(
Here's the race website: http://www.dcchallenge.org/race/