Here's a short list of my favourite tools for OS X:

• NetNewsWire 2 - Though version 2 is still in beta I prefer it to the old version for the new version has many very welcome improvements.

• LaunchBar - A pretty good application launcher. However, the counterpart QuickSilver isn't bad, either. And it's free, too.

• Adium - Nice instant messaging client. Supports most protocols. Highly customizable.

• TextMate - Very powerful editor once you've discovered all the features :-)

• Skype - Very nicely ported to OS X

• PDF Browser Plugin - View PDFs in Safari

• jIRCii - Nice IRC client written in Java.