I've put together a very preliminary file of all the core CSS styles I could find for the various page views and such for the Sandbox Theme: There is a link to the CSS file at WordPress.com Custom CSS - All The Styles for the Sandbox Theme.
Please help everyone by leaving comments on that post with any styles you want to add, think are missing, or wrong.
After an initial dig into the Sandbox Theme, kudos to Scott and Andy for adding amazing levels of customization. I'm starting to put these thoroughly to the test, so we shall soon see how quickly I can screw up my WordPress.com blog. ;-)