I'm going to join in since I've been using a pebble for years with great enjoyment.
I treat it as a secretary. I think of different communication media as having different urgencies / time constants. Emails are a daily report. My phone's notifications are an hourly report. Notifications which I forward to my watch are the instant things. Be sure to mercilessly "mute" most apps from bugging you on your wrist. With this setup, I never feel the urge to check my phone. If there is something important, it would've buzzed my wrist.
Here are my subjectively appreciated apps
Homescreen: Fairweather. It is information dense display of weather, sunset time, pressure, vis., etc.
(Top) Button shortcut: Forecast weather. Shows a probability of precipitation over the next 24hrs (I donated for data from forecast.io). Great for avoiding the rain when walking the dog / biking home / etc.
(Bottom) Button shortcut: A bus/train stop info panel. It uses the phone's GPS to tell you when the next buses/trains are coming. Handy for when there is a stop within 100 feet of the bar and you can know if you want that extra beer or not.
Timer/Multitimer are great. Alarms for waking up are great. 7minute workout app is great.
- Compass - for compass and the ultra-cool switching between normal and "in-flight HUD" display depending on your wrist orientation.
- GPS Bookmark - lets you bookmark the location you're standing in right now, and later display the direction and the distance to that location. It uses the compass on your watch and your phone's GPS. It works on GPS coordinates, so it doesn't require you to have any Internet connection. I found it extremely useful when I was in Shenzhen, China - I bookmarked my hotel and work, and used the third bookmark slot (you have one slot per button) to record temporary locations like the metro station I just got off from. It was really invaluable for finding my way back from wherever I ended up going.
- PebbleTasker - like the name suggests, it lets you call Tasker tasks to Pebble. I.e. you can make Pebble buttons do pretty much anything on your phone, without having to write an app yourself. You can bind some to each button, and then also use a list menu for more. The bindings can also be dynamically configurable from within Tasker, if you feel like making e.g. location-aware actions on your watch, or something.
- AutoPebble from AutoApps plugins for Tasker - something similar to PebbleTasker, but more advanced - you can dynamically configure the contents and behaviour of the watchapp from Tasker. A bit more difficult to set up, but also much more powerful. It's probably the best option if you want to have whatever the data you want on your watch, and in the way you want it.
What apps do you use and can recommend?