Options for established programs with elementary options:
http://www.mathleague.com/
http://www.moems.org/
http://www.continentalmathematicsleague.com/
I'm pretty sure all cost money.
I lead a math club and a computer programming club at my middle school (I teach math), but it's just me coming up with brain teasers and puzzles and activities for the kids each week. The school doesn't have budget to fund anything more than that.