there are lots of varitaions of filters. It is very simular to a hang on back filter but it's a few inches higher and the pump is in the tank. I have seen a custum set up like this but yes that exact configuration is not used much.
please keep suggestions coming... I'm going to tesco this weekend to pickup some new sponges and scrubbies and going to the LFS to get bio balls and ceramic rings. Just hope they all fit in the filter box...