[Suggestions] What are some of the best/beautiful icon packs you use?

The title says it all really. It would be nice if you can suggest some of the free ones even though, I don't mind shelling out money for the really beautiful ones. Thanks!

Info: I use Nova launcher so icon packs that specifically do NOT work with Nova would be of little use to me. But, since it might be useful to others, please feel free to mention such icon packs anyway as long as you _also_ remember to mention compatibility.