What works:
Stuff toys - My dogs love to play operation, shread them and turn them inside out.
Ice cubes - Like clock work, as soon as they hear the ice maker, they come running.
Kong - peanut butter at the bottom or treat at the bottom, then shove it with a giant ice cube, it'll take them sometime to lick /melt the ice to get to the good stuff.
Semi work:
tennis ball - Mocha love me throwing the ball, but he'll bring it back half way, make me go after him, and when he's had enough, he make me to go fetch the ball.
No working at all:
plastic toys, like giant knobby ones, or any weird shapes, they won't even look at them.