Last week GrabCAD very impressively hit 400,000 registered Engineers and Designers. 100,000 more in less than 3 months!
In the the AEC space, new arrival BIM Object (under a year old) has just passed a 100,000 downloads of their intelligent smart BIM object's (a very different and impressive approach which I will write more about soon).
Then there is Sketchup 3D Warehouse, once own by Google, now by Trimble, this is filled with all types of models, mainly buildings made in Sketchup. They keep quiet about the number of models but from my own research I estimate their is around 5.1 Million models in the database!
In the games space, Unity Asset Store continues to grow at a phenomenal rate and is well used by Unity3D designers and developers.
And finally, the long time Turbosquid continues to be used in the media and entertainment space.