An often forgotten AutoCAD command is Copytolayer, which will allow you to copy one or more objects to a different layer. You can choose to copy them in place or move the copy just like the regular Copy command. To choose the destination layer, you can either pick a reference object or select the layer name from a list.

Notes from Cadalyst tip review R.K. McSwain: I find a lot of AutoCAD users are not aware of the Copytolayer command. It's very useful if you need to make a copy of something and put that copy on a different layer.