Spinthrift offers a simple and easy to use solution for rotating objects with the mouse. This is a collection of several self-contained C# scripts each offering a small variation on the task at hand: click on an object then drag to rotate it during runtime. Each script is easy to use, simply attach it to the object you wish affected and you're off spinning, of course there are several parameters you can set to change behaviors including rotation speed, return speed, axis rotated, and mouse button to use.
