Applejack was recently updated to add compatibility for Leopard. This is a MUST-HAVE troubleshooting utility that runs in single-user mode. It does many of the things that other utilities like Onyx and Ice Clean do, but is less encumbered by running in single-user mode. You can also use it to help solve issues that may be preventing you from loading the GUI. This should be the first thing anyone installs in OS X when they first get their Mac or reinstall the OS.
I just ran it myself since some people report it leads to noticeable performance boosts that you won't see doing the same tasks with other utilities. It may just be my imagination, but it's only been a week or so since I last ran Ice Clean and using Applejack seems to have made my system snappier than ever.