Necco wafers are a favorite of mine for targets. I stick them onto a target board by using pieces of folded over masking tape. When hit they disintegrate, so no clean up is needed. Last summer one of the guys at the range had brought along a bag of those "Dum-Dum" lollipops; like a Tootsie Roll pop, only smaller. They started an informal competition with rifles at 50 and 100 yards. They stuck them between the cardboard and the wooden frame of the target board so that they stuck out on the sides. When one got hit, it disintegrated. Very challenging, since you can barely see the things without a scope.
Another thing to try is "target poker." Shuffle an old deck of playing cards and stick them to a target board so you can see the faces. Each shooter gets five shots for their poker hand. Best hand wins. Use a magic marker to cross off the existing bullet holes and you can go again.