Many math clubs have started already. This web site lists all major math contests in US. And tons of resources for preparing for them.

http://k12mathcontests.wikispaces.com/

Nice resource, mbark. Although it is not a comprehensive list, because it doesn't list things like Rocket City, Purple Comet, Sigma competitions in Middle School.

cym, it's a wiki space, so I think you can edit it to add those. It'd be much appreciated!

Thank you mbark for that link.