I would recommend Boomkinator or Quartz.
Power Auras is a great one, too, but I`m too lazy to mess with it.
There's a small problem with the Boomkinator add on just looking at the description. It says that during eclipses, star surge is dimmed. From what I've read here and on EJ, that shouldn't be the case. You want to cast starsurge everytime it comes off cooldown as it's our most powerful nuke. I think using that add on would just end up confusing me with that error.
It isnt anymore, they fixed it. Once starsurge is up, it appears, during eclipse or not. Its dimmed when its on cd, like everything else.
Boomkinator, for me, is a great reminder. From time to time I forget to cast Starfall.
It has a big problem, though. It doesnt know the difference between your dots and the dots of another moonkin. So, if you are using Boomkinator to keep track of your dots, forget it. When another moonkin cast a dot, it will think it was you and mess everything up.
Thats why I said that, for me, its a great reminder of CDs.