Quicksilver : like that other app that sat in your menubar and you could hotkey into it and type what you want and it'll take you right there.. yeah, it does that. only Qs doesn't take up any space anywhere, and I like the way it works more. you can use arrow keys to browse the heirarchy of results based on what you typed in, and it just 'feels' nicer. it practically begs you to play with it more, it has such a shy yet approachable interface.
SideTrack : it's an alternate trackpad driver (really only usefull for the notebook users) that lets you define scroll areas on the trackpad and do other very helpfull stuff that the mac's trackpad has been lacking. quite nice.
Notational Velocity : it's a note-taking program. That's all it does. it sits in the background waiting till you hit a hotkey, then it pops up and you start right off typing in the note's subject. tab and it takes you to entering the note body. the great thing is, it does active filtering of the existing notes based on the subject you are typing. at any moment you can stop typing the subject and hit tab to start editing (defaults to append so you can just get right to typing) the currently selected note. If you're done with the subject and there's a note matching that subject selected, but you want to make a new one, hit Cmd-D to deselect it and then tab right into a fresh new note with this subject. *Very* well-writen program for those sudden "Oh, yeah! I gotta right this down RIGHT NOW" type of thoughts. 100% keyboard-driven interface to pull it up from background and enter/edit notes so you can get the inspiration jotted down quick without getting interrupted/distracted.