Best animation plugin that works with the new 2D stuff?

Hello, I'm looking for a plugin that can help me create some animations. We were searching for some but most of them work with the old way .. having 3D planes etc.. I would like to work with the 2D stuff since I believe unity is doing a great job with that. So I would like to know.. is there some plugin that will let me reuse the animations like unity does? And that would let me swap sprites easily as well? Thanks!!