Complete game-changer. Practically allows regular Android widgets to be displayed on the watch.
Takes a bit of configuring, but it's soooo worth it!
I have Google Now, Spotify, Spotify remote (for my desktop), FlightTrack (next flight information), Widgetsoid † (airplane mode, silent / vibrate mode etc), Facebook, Google+, Twitter and a button to put my desktop to sleep (via Tasker SSH Command Launcher).
I also keep this app open on the watch so it's immediately there when I double-press the watch button.
If you have ideas for other interesting widgets to use, leave a comment below.
† Needs "Dim screen" config.