Sometimes you need to see what's wrong with a WordPress install, and you need to see it fast. I've had a set of hacks around for a while to do that, but finally started combining it into a WordPress Debug Theme. This theme is quite simple for now, as it only does a few things, but does them quite effectively.
Visualizes for you all kinds of important data about the page you are looking at. All kinds of fun for us WordPress nerds.