This script adds some simple missing hotkeys to the Animation window in Unity.
Create an Editor folder in a location of your choice in your Project view and place AnimationWindowHotkeys.cs inside of it.
P - Play Animation I - Previous Keyframe O - Next Keyframe
These can be changed by editting the [MenuItem()] inside AnimationWindowHotkeys.cs For more information on this, visit the Unity Documentation
Note: Because of a bug in the Windows editor, you will have to use Shift+Key to get the hotkeys working.