We actually experimented with using this for the rebuild of TimeFrame that we are putting together in our free time, but now we are considering using it in Lacuna Passage as well. It's a great way to "capture" a physics event and replay it exactly the same every time. In the past we have had to use complicated animation exports from 3ds Max or just let our physics events react differently every time with Unity's physic simulations. Not only is this a simpler process, it also greatly improves your game's performance since it doesn't require physics calculations.
Mega Scatter - by Chris West
I have been using this plugin in tons of great places. Most notably, for mass-placing rocks around our Mars terrain. This is another very polished plugin from the makers of MegaFiers, the Unity mesh deformation system. The scattering options are extremely customizable and their user support is excellent. The only downside we have found is that large scenes start to present scattering issues including slow down, but this system is perfect for scattering objects around medium and small scenes.
Shader Forge Beta - by Joachim Holmér
We already mentioned this one in a previous post back when it was still in Alpha, but now it is in Beta and available on the Asset Store officially. I can't say enough good things about Shader Forge. The developer is extremely active in improving this visual shader editor and we use it for all the shaders in all of our projects now. This isn't just a tool, it's an investment in the quality of your game's art. If you come up with an awesome shader you could even put it up on the Asset Store yourself!
VPaint: Advanced Vertex Painting - by Valkyrie Entertainment
This plugin is super useful when combined with Shader Forge. We are working on some shaders that utilize vertex colors for texture blending and with this vertex painting tool we can experiment with these blend settings without having to swap back and forth between Unity and our 3D modeling applications. As usual, some of the best plugins are the ones that save you time and VPaint is no exception.