I agree with Sam about helping students explore in more depth rather than moving on. Sometimes just changing the magnitude of the numbers works.
I also like to push their mathematical thinking, having them find patterns and make generalizations. After finding a pattern: What is the pattern? Why does it happen? Will it always work? How do you know if you can't test all possible cases? These kinds of questions often send the brightest off on fascinating explorations. Be sure to give them time to share what they find out.
Last year I had a conversation with two other mothers about our own children's math experiences. All three children were strong math students who got pushed ahead. They all took traditional honors or AP math courses in high school. As they headed off to college they each had said to us that they did not plan to take any more math courses than were required. There's something wrong when our best and brightest math students lose interest in math. I only wish my daughter had gone through the courses that are in place now. I think it would have made a difference in her attitude. Nancy