Or just undercut them all and charge $20. I charged $14 - only a high school student, after all - and it was still double minimum wage.
Construction over the summers is also pretty nice money.
But here's the highest-paying job I've ever come across: waiter/valet at a swanky restaurant. These positions will be few and far between, and you'll have to get lucky and present yourself just right when you apply for the job, but man, if you're getting $100 tips and making $20,000 in a summer, you're pretty much set.