This was the fruit of about four hours of trying to figure out how to do this, it's a simple script that reads the folder id of the page the block is displayed on, then lists the pages inside that folder. I mostly made this for use as an index page for most of the sites folders, however I am thinking of doing up a sidebar version at a later date.
Source code: http://www.xershade.ca/content/articles.html/programming/invision-power-board/folder-index-block-r1/
Demo: http://www.xershade.ca/content/index.html/