Small but Useful
Raging Menace has a bunch of little Mac OS X programs by Alex Harper, and very useful they are too. SideTrack is a replacement driver that lets iBook and PowerBook users reconfigure the trackpad to provide scrolling areas, tap-to-right-click and on. MenuMeters provides a set of neat meters for memory, CPU usage and so on, that don't take up much screen real estate; I've found it particularly useful to confirm that it is indeed more memory that I need, not a faster processor (when the paging indicator goes off the scale, that's a hint). I'll probably have a look at SleepTight at some point too. It gives Jaguar the Panther-like functionality to lock the screen when the machine sleeps. Handy when you're carting the machine round, but I'm only using the iBook at home at the moment, so I don't really need it just yet.