Aggro circles addon?
 

Any addon that will show mobs aggro radius?

Not possible. You cannot draw anything in the 3D world and cannot determine positions of anything on screen that is part of the 3D world. The UI technically doesn't know the 3D world even exists. Nameplates and chat bubbles magically get position data that cannot be accessed and mouse interactions are completely hidden.

As said you cannot have this in the 3D world, however you can have something like it for Minimap with Chinchila minimap addon.