My 8 year old son wants to start a business. What kind of business should he start?

One congratulations on having a son that wants to start a business. That is absolutely fantastic. Yes, your son could sell lemonade or do chores for his neighbors.

I have a little bit of a different answer. Partly due to reading the Last Lecture, I would suggest letting your sons imagination run wild with potential ideas. At that stage it does not matter if he succeeds. If you encourage him to think big it will have such a greater impact than a lemonade stand.

I clentch my teeth every time I volunteer at schools or listen to parents squelch their child's view of what is possible. The side effect to this can be seen later when he/she is in college or at work and can only see why somthing is not possible instead of thinking creatively. Selling Girl Scott cookies and making lemonade stands aren't the only ways to foster entrepreneurialism in youth.

Best of Luck!