A favorite Nature Spirit:
I'm big on Trees. :)
There's an awesome ancient Oak tree on the campus on my local university. He's huge and his branches are so heavy that they're slowly growing towards the earth.
As a spirit, he's sweet and graceful. And slow, but most Oaks are.
There's also the Spirit of a spring near here. Legend has it that a Spanish Saint created it to bring water to the people that were there. When we first moved here, I left an offering there to the spirits of the city to introduce myself. It remains a favorite place to commune.
Note: the oak tree in the photo is not the tree in question. That's the Angel Tree in the Carolinas. Sadly the surroundings of the tree on campus don't make for the best photos.