Download Jiggling Free Unity. 

Make your objects jiggle in two clicks!
Jiggling is a package with components simulating jiggle animation using just rotation and scalling in a smart way.

Link to community forum thread

You can archieve cool effects with it, fitting pretty well to cartoon like graphics.
Just add component to your game object and play with parameters.
If your object is dynamically scalled or rotated in game you can always use parenting to add jiggle effect to it.

Main features:
● Includes interactive demo scene
● Includes full source code
● Scripts are commented in detailed way