Well I have a simpler version of that on http://bitcoin.clarkmoody.com/order-book/
but the good thing about my calculator is that is computes the slippage you will incur based on the current order book. I am also working on a version that incorporates more options - coming soon.
You have me pretty close to stop posting!
What you did there, is what provoked me to finally find something.
Still get to post!