I have written a .NET app for trading on Mt. Gox using their APIs. I spent most of the last 2 days writing it and I am pretty damn proud. There is a writeup and download link here.
Basically, it gives you the ability to schedule trades, remove trades, analyze the depth of the market, see how many or how much is in front of your trades, further there is also a stop-loss monitoring feature that can kick in if the price moves too much. Happy downloading, I have set up an email for feedback if you have any constructive