Elementals as Nature Spirits

I think one could way to make your setting more unique is to have some elementals actually living in the world. They would be nature spirits, and might even be worshipped by local tribes. I'd give them more intelligence than your typical summoned elemental, of course, so that players could interact with them.

This was done in Exalted and Avatar: The Last Airbender (and a bunch of Eastern myths), but I don't know that it's been included as part of a vanilla European fantasy setting. I think it would be a cool variant, even if it's only in one area of the map.