More than two years ago, I suggested a visit to the Illusion of the Year contest (see above), sponsored by the Neural Correlate Society and Vision Sciences Society. Several years and contests have passed, and it is perhaps time for you to revisit the contest.
The current website shows this year's top finalists (2009) and the awards they won. The First Prize Winner is quite unusual...watch the full video to get both the effect and underlying mathematical explanation.
You can access the ten entries here, brouse the rules, or perhaps work with creative mathematics students to enter something yourself next year?
Also, while visiting, check out the full site as well. You can browse the "best" of past year contests, see the top-related visual illusions, explore the neuroscience underlying visual illusions, try random illusions from creative people internationally, visit the giftshop, and find additional references to sate one's visual illusions' appetite.