Here are a few ideas:
Browse the Table of Contents of mathematics journals.
Browse the Shelves! Scan the titles and/or thumb through books on a topic you like (such as probability, algebra, game theory).
Check out the websites tab.
Talk to your professors; sometimes just talking to someone else can spark a great idea!
Some Relevant Call Number Ranges for Math:
QA 75.5 - 76.765 -- Computer science. Computer software
QA 150 - 272.5 -- Algebra
QA 273 - 280 -- Probabilities. Mathematics statistics
QA 440 - 699 -- Geometry. Trigonometry. Topology