As a quick note, and you probably already know, a way to make tons of different rocks quickly in Blender is to use the displace modifier.
First you create a sphere, or I like to create a subdivided cube, then an empty. Add a displace modifier to the sphere, or cube. Create a new texture for the displace modifier and set it to 'clouds' type. Then back in the displace modifier properties set the 'texture coordinates' to 'object' and select the empty you created. Modify the texture settings and the modifier settings until you get something you like. Then just duplicate the sphere, or cube, and move it. As you move it you'll notice the displacement modifier effects it differently depending on its world space coordinates relative to the empty. Duplicate your sphere or cube to create as many rocks as you need.
As an added bonus you can move around the empty and scale it to fine tune your displacement.
This is the method I used to create the asteroids in Space Rocks. They all use the same textures, after texturing I did the displacement modifier and duplicated a bunch of'em to get a bunch of different rocks to randomly spawn.
Took minutes to make all of them.