You could try throwing a ball against a wall and catching it with the other hand.
To make things more unpredictable, stand a couple of paces away from the corner of the room and throw the ball at the corner.
I've also heard great things about a "reaction ball". It's a strangely shaped ball that will bounce in many different, and random, directions making you work a lot harder to catch it.
I first came across this as a cricket training tool, but would work well for anyone looking to improve hand eye coordination.