CloudApp & Droplr: Sharing documents and other files. CloudApp has a great link shortening feature (I use the keyboard wherever possible) but is limited to 25MB files. Droplr also has the much better iPhone app.
Dropbox: Using it with 1Password, PKGBackup, and other things that should be stored and accessed wherever possible. Also great photo gallery implementation for simple photo sharing
Adium: The one and only IM
: For displaying the current track
ControlPlane: Automatically switch location by rules (‘WG’ is the German abbreveation for ‘flat share’ though)
TextExpander: Save your time - use TextExpander!
Blast: Keeps track of my recently changed/opened/created files. Very good when I’m downloading tons of documents for university
Evernote: Note taking accessible over Mac, iPhone and internet
Caffeine: Prevents my Mac from falling asleep
SlimBatteryMonitor: Does what the name suggests
Then the usual: Wi-Fi, Bluetooth (with MagicMouse connected), Time Machine (damn! how I hate that exclamation mark appearing on Lion when not backing up for 30min), Clock and Spotlight.
I got some other apps running like Alfred, Default Folder X, BetterTouchTool and Divvy. I would have put them into the menu bar but the problem is my Mac being a MB13,3inch model. Therefore space on the menubar is rare.
(From gramuel)