Commerce Product Clone
This module makes it easy to clone products by simply pre-populating the product creation form with all of the data from an existing product. Someone will eventually come out with an entity_clone module that will make this obsolete I'm sure. I built this to take care of some immediate needs.
This module is very similar to node_clone (clone). I started from the ground up and implemented the different pieces from that module that applied to what I'm trying to achieve here (with many modifications, or course). Regardless of how different or similar this module is, I am thankful for the efforts of the node_clone authors.