From left to right:
Encrypted DNS lookups (useful for public and corporate networks)
Quick and easy access to edit your /etc/hosts file
App launcher / Do By Searching
SSH Tunnel Manager:
One-click start/stop for tunnels... again, useful for public and corporate networks (paired with FoxyProxy for Chrome)
Cloud-based file syncing
Remote access for the iTeleport client (VNC-like screen sharing client on my iPhone)
Instantly uploads all the screenshots I take to tomfro.st, with optional editor and stuff, and puts that URL in my clipboard. That's where the above screenshots come from. (There's a free version in Ruby, but for a buck or two the version in the app store has WAY more features)
Quick and simple way to grab the hex code for any pixel on your screen, with magnifier.
Just a helper for the desktop app
Remote access for Splashtop. Only because there's no iTeleport for my Android/WebOS tablet.
Display prefs built into mac
The network graph, RAM meter, and CPU usage graphs are all from this. iStat Menus offers way more, but these are the ones I find useful.
Time Machine, Bluetooth (with low battery warning..), wifi, sound all built into Mac
Clock/Calendar comes from there
. If you click on it you get this, which I couldn't live without:
...and then spotlight.