QuickTime Pro
No-one dealing with DV should probably be without this tool. For 30 EUR you can manipulate QT metadata, do copy-paste editing and basic recording and transcode to hundreds of different codecs and formats including H.264 and 3GPP. Simply priceless. Buy it and ask questions later. :)
Blender
Blender's on of those "too good to be true" apps. For the price of nothing, you get a powerful 3D modeler and animation package, renderer and extensibility through Python and a compositing environment / basic NLE. Plus it's got a wonderful community around it. Brilliant.
BBEdit || TextMate
I'm not one of those "old time" BBEdit users (I used BBEdit Lite quite alot, but not for any kind of coding), but I have to admit it's the most well-rounded editor out there for the mac, plus the most mature. While I still think the JEdit is the coolest editor of all time, on the Mac, I use BBEdit.
Yojimbo
I have mixed feelings about this app. Any kind of organizer expects a certain degree of organization from it's user, except for Stickies, which I had been using for many years. But then you come to a certain point where You just need something more.
RapidWeaver
I don't use it anymore, but still highly recommended to anyone who gets an allergic reaction to the "design" in web design. ;)
NetNewsWire
NNW's interface is by no means groundbreaking, but it works better than anything else I've seen so far.
DeskShade
Definitely more of a "nice to have" app, but cool nevertheless. DeskShade makes managing your desktop background collection a breeze + has some handy features like hiding the desktop and locking it with a password. It's very affordable too.
Menuet
Menuet's actually more useful than DeskShade, but still in the "nice to have" category. It allows you to control iTunes from the menubar and do many other cool things.
Quicksilver
They say you can't teach an old dog new tricks, but sometimes the trick is so cool that the dog just goes and learns it anyway. Quicksilver propels productivity such a level that you'll quickly start thinking how you managed without it.
PHP Function Index
I think PHP has wonderful documentation which makes it even more important to always have it at yourfingertips. There are alot of widgets out there that try to do the same thing, but none of them match the speed of PHPfi. If you do PHP on your Mac regularly, do yourself a favor and get it.