Your question is right up my alley, so to speak: most CAD programs can do this. In DataCAD they are called symbols, and they can be anything you can draw. The copies can be rotated, mirrored, etc. very easily while you insert them or afterward. It is mainly 2D, but it has so-called 2.5D (entities created with a Z-height) and full 3D abilities. There is a demo version that is free: http://datacad.com/demo/index.html
A 3D program that can do this is SketchUp, which has a free version. In SketchUp, they are called components. Again, they can be anything that you can create, and then can be copied and repeated, all over the place. http://sketchup.google.com/
SketchUp is very
easy to use.
In both programs, these entity groups are "locked" in the main drawing, but if you need to, you can edit them and the changes are automatically made in all instances. As an example, my SketchUp model of the open source CarBEN EV (at the end of the Super Efficient Car thread
) is made up of two components -- each half of the car are mirror images and any edits on one half immediately happen on the other half. Also, the five 3D figures are all a component: the front three are the same, and the fourth and fifth ones are slightly reduced in size, but otherwise identical copies.