NGUI Is a great replacement for Unity's native GUI system. Unity's GUI system has performance issues, especially on mobile devices.
Uni2D Turn your drawings into "GameObject" by a simple drag and drop and then add the physic automatically without any use of a 3D modeling software. Major features of
PlayMaker is a Finite State Machine with a visual editor. It is the first plug-in you should get because you act quickly create behaviors wit the visual editor and the action br...
2D Toolkit fixes Unity's lack of 2D sprite support.
Little Vector Library
Draws 2D graphics onto textures and images.
RageSpline allows you to edit vector graphics in the Unity editor. Also, consider the RageSuite that includes RageSpline.