Quoted from jgentry:Slimer
captive ball
3 ball captive ball
subway lock
magna slings
I wouldn't consider all of those toys or necessarily things that interact with the ball, but the Scoleri Brothers definitely interact with the ball that I'd add to the list (most first time players are even thrilled to see them pop up unexpectedly).
Hopefully there are interesting "force" magnets under the SW field we haven't seen yet. Would be a shame if multiple magnets aren't hidden on a modern SW game.