Adium instead of iChat
It is easy to get sucked into Apple's applications that come with OS X, particularly when you compare them to the lame ones that Microsoft includes with XP. But there are ones that are better.
I wasn't all that keen on using IM a few years ago, but it was convenient for a few friends I had. When I first launched iChat, I was quite impressed. I've been using it a few years, and became surprisingly fond of it.
Then Tim Bray recommended Adium, and I took a look at it. In short, if you like iChat but don't use the voice capabilities, you may love Adium. You can make the contacts window much more compact, you can have all your chats in one tabbed window, Adium integrates many more IM services than iChat, and you can change the color schemes easily. If you have a long list of chat partners on different services, Adium will cause you to remove iChat from the dock.