Hey. A good website is cuttheknot.com. It contains alot of material that I'm sure you would find intersting, but most of it isn't printable. If you want printable material, I would sugest the website CEMC - Past Contests - Mathematics and Computing Contests - University of Waterloo where you will find math contest you can print off. Also, if you do some digging in the resource section of the site, you should be able to find euclid workshops, which are instructive.