I didn't find them this year but no one's mentionned them and they are so good that I have to.
First, Mellel is by far the best Word Processor that I've ever owned. It blows the doors off all the others. Start using it and, little by little, you will come to understand what I'm saying.
Second, MacJournal just keeps getting better. The more I use it the more I realize that it does exactly what you want a journal to do, no more and no less. I just hope the new developer doesn't get too ambitious and spoil it with new features. This one works so well because it adheres to the KISS principle.
Third, Voodoo Pad is an really usefull application for quickly and intuitively building a WIKI on your computer; connect all the cool things that you didn't realize were connected. It isn't as irreplaceable as the previous two apps, but it's quite cool.
These three applications are enough by themselves to keep me firmly committed to OS X.
A Dozen Mac Gems Unearthed In 2005