Try to break down big topics into smaller subtopics or related ideas so that you give yourself as many choices or thoughts as possible. In this manner you will be able to associate thoughts together more quickly and actually start to generate the storm that will help you find the right topic. Then proceed to the idea of approaching another person or group to bounce your ideas off of them and find out what they think about your topics. Not looking for criticism, but for fresh new ideas or topics or ways at looking at old topics or ideas. By establishing that interaction with other students or friends you can more quickly strike sparks and ignite the flame of new thought.
Many sparks contribute towards a bright and powerful bonfire.
Many friends can contribute towards a whole plethora of ideas. This is also a good method for refining ideas that you have or for rejecting those topics for papers that might not be feasible, or less than appealing to an audience. The third suggestion for brainstorming is by far one of my favorites. It involves sitting down with the primary textbook for the class and looking at the chapter headings in the table of contents. Very simple really.