i have heard of ping pong balls, a piece of a fake plant and let it float around (they will catch it and swim around with it), a film canister filled with gravel so it sinks, bouncy balls (i think thats what they're called! those little rubber balls that bounce), dome type of hoop and suspend it in the water (they may like swimming through it)...i have tried the fake plant and the film canister and my oscars dont seem to bother with them. My big girl is quite happy digging through the gravel until she reaches the bottom of the tank.
