Adium - The best Mac IM client for multiple protocols. It’s also highly customizable.
- New mail client based loosely on the Tweetie interface. I’m still attached to Mail.app, but Sparrow is a very interesting new take on e-mail. I especially like the Quick-Look-esque message viewing.
- The official Twitter app for the Mac, formerly known as Tweetie.
Caffeine - The app to keep your Mac awake. It keeps your computer from entering sleep mode. I use a custom icon that fits in a little better with the others.
CloudApp - This app is the easiest way to share files and photos. Drag them onto the menubar icon to instantly upload. The link is copied to the clipboard automatically.
Carbonite - Awesome online backup.
Keychain Access - Lock your screen and/or keychains easily. Turn this on from the Keychain Access utility’s preferences.
Spaces - OS X’s virtual desktops. I use four. I almost never move between spaces using the menubar icon, but it’s a good indicator to see what space you are on at all times.
Time Machine - Apple’s backup utility. I recommend using it together with SuperDuper, which makes bootable backups of your entire disk.
Airport - For connecting to wireless networks.
Volume - For adjusting … volume (or seeing what level it’s currently adjusted to).
Input menu - I often switch between English and Chinese Pinyin input, so I need to see which I’m currently on (although I use the keyboard shortcut to switch). This is also good for opening the character viewer or keyboard viewer. You can turn this on by going to the “Input Sources” tab in the “Language & Text” preference pane.
Battery - Pretty self-explanatory.
Clock - I’ve turned on both the day of the week and the date.
Spotlight - I actually don’t use Spotlight all that much. In the past, it has mainly been replaced by Quicksilver or Launchbar, but I now use Alfred (with the “Powerpack”) for all my launching and file-finding needs.
(From Sam)