FeedBeef Pop Art
Simple and easy to use. Best UI for calculating shipping rates. It's an install and forget sort of app with little set up after install. Excellent developer communication as well.
I installed this App recently and it has great potential, I had a few issues with integration but Richard is super helpful. Great support.
Sorry to hear about that. I'm here to help! Is the entire page blank or just the part where the ship rates should be displayed? If you can contact me with a link to your cart page that would help tremendously.