What does he know as of now? I mean, the sky is the limit! If you know how to clicker train / shape behaviors then you can train him to do anything. Turn on or off the TV! Pick up his own toys and put it in a basket.
I've been trying to think of ways to try to combine the different things he knows now into something cool. I think he needs to get better at retrieving first though, because a lot of my ideas include that.