MathPro Press is a website that more mathematics teachers need to know about..and visit.
Its goal: To provide online information about mathematics problems, mathematics problem books, and mathematics problem journals. So, if you are looking for good problems (usually non-standard), this website is for you!
First, browse through its long list of MathPro Press Books (very good!), a useful compendium of mathematics problem books (great!), updates on recently-published problem books, and books about international mathematical olympiads.
Second, MathPro Online is an online searchable data base of more than 20,000 mathematics problems. It should keep you and your students busy for a while.
Third, it offers links to web sites specific to mathematics competitions in the United States.
Fourth, the site lists elementary mathematics journals, journals with mathematical problem columns, journals that review mathematics books, and best of all, journals with online problem columns.
And fifth, the "kitchen-sink" portion offers general resources such as an online mathematics dictionary, online glossary of technical notation, state mathematics guidelines, mathematics summer programs, and summer camps for high school students.