@cparki3 for reference: https://github.com/nickgravelyn/UnityToolbag/tree/master/SortingLayer
Note that it's not updated for Unity 5 so the change from simple small ints to full sorting layer UIDs still applies as long as you're using Unity 5.

SkeletonRenderer's inspector code for sorting layers works correctly with Unity 5 though, if you're interested. See here: https://github.com/EsotericSoftware/spine-runtimes/blob/master/spine-unity/Assets/spine-unity/Editor/SkeletonRendererInspector.cs#L105