You can get cake pan sets to do this too. It comes with three shallow 8" round pans, and this plastic template kind of thing that you use when adding the cake batter to the pans, so you actually bake each layer of the cake with the two different batters (instead of baking the cakes normally, and cutting out the middle bits). Very easy to use, as you don't need to have each of the cakes be the same height (if you're prone to uneven layers like I am).
But this is a great way to do it, sans the expense of fancy pans. Great thinking!