If you have a 50mm lens (or any kens for that matter) kicking around reverse it and push the front end of the lens against the body flange so that no light gets in. You get an incredibly thin DoF. It is best if you use the lens wide open or pretty near.
These shots were taken with a 50mm Zuiko f/1.8 and you can pick them up for next to nothing. If you want to get really snazzy you can buy a reversing ring to suit you camera system. I did not take as much care as I should have with these but you get the gist.