Accessible through Galileo's A-Z list of Databases:
The Math Forum: Student Center (and Teacher's Place) offer research options, problems of the week, and more. The Math Forum is a leading center for mathematics and mathematics education on the Internet and was once a subscription service before joining Galileo.
The National Science Digital Library (NSDL) is a STEM resource and has mathematical resources you may find useful. Topics include: Mathematics, Algebra, Calculus, Functions, Geometry, Measurement & Data, Numbers & Operations, Ratios & Proportions, and Statistics & Probability