Version 1 of my UI. Using Version2 now which is slightly different (No black bar across the bottom, items like the Panel Datatexts (gold, sp, etc) are revamped. I'll update a SS later. Available on WoWI

Does anyone have a good recommendation for an addon to maximize Nature's Grace uptime? The challenge of course is its an internal cd. Some kind of timer and preferable power aura type pop up would be preferred.

You may want to check out NeedToKnow (link) - it's able to track all kinds of cooldowns and the author recently added the option to reset cooldowns based on the presence of another buff (eclipse resetting NG cd for example).

If you never play moonkin, static cooldown trackers like ForteXorcist (setup) or ICDBars do the job just fine
As for PowerAuras, you can vote for the Feature Request to track internal Cooldowns at http://powerauras.wikispaces.com/

Or maybe use Koko SpellOverlays to tune up the blizz-effects.