As the title may suggest, what is the WeakAura display that you've made yourself that you are most proud of?
For me, I would have to go with the Time-Lost Artifact notifier.
Sometimes, I put the trinket on to get to the Timeless Isle, but I forget to replace it, and my DPS suffers because of it. SO, I decided to make a WeakAuras interface to warn me when I have it on, displaying in big text to remove the trinket, and it goes away once the trinket is off. That way, I no longer forget about replacing my trinkets!
If you want, I can paste the code for others to use.