DiskWarrior, my personal favorite disk repair utility (especially if the problem drive is the startup disk) has just been updated to Version 4.1. The new version is now fully compatible with Leopard (there were some issues with repairing disk permissions on a Leopard startup volume), so if you rely on DiskWarrior as an essential part of your Mac Toolkit arsenal (as I do), you can rest easy.
Alsoft has also introduced some additional Leopard specific repair features in DiskWarrior 4.1. What has me the most excited is the ability to repair directory hard links. Hard-linking is a key part of how Time Machine creates back-ups. How the process works is complicated (although this article does a very good job of trying to explain the whole process), but it is a vital part of Apple's back-up system. The ability to repair directory hard links means that DiskWarrior 4.1 should be able to at least attempt to repair a Time Machine volume. That has actually been my only concern about Time Machine -- what happens if that volume become corrupted or wonky? I hope I don't find out first-hand, but I'm glad some options exist.
Current users will soon be able to download an update CD directly from Alsoft's website that will create a new DiskWarrior startup disc (in the event that the drive needing repair is the startup volume and you don't have access to another Mac). However, please note that the update will only startup the same set of Macs as your current CD. So if your current CD will only boot up to June 2007 MacBook Pros, the update CD will not allow that disc to be used with a November 2007 MacBook.
One other caveat, if you want to run DiskWarrior 4.1 from a version of OS X other than Leopard (say, Tiger), two features will not work. You will not be able to repair permissions of a OS X 10.5 startup disk and you will not be able to rebuild a FileVault created under OS X 10.5. So if you need to repair a Leopard volume, it is best to either run the startup CD or access the drive from a computer that is also running Leopard.