One or two year ago I organized a "Manipulate contest". Only interested students signed in. I gave them two lectures on the use of Mathematica, then I helped each one of them to develop her/his Demonstration. Profesors voted for the best Manipulates, and we gave them I prize (books, Mathematica license, MathLink for Excel license) at the end of a conference by Ulises Cervantes (Kernel programmer of Mathematica) in our Campus. Here are their Manipulates, not all of them work as expected, but it was a great expirience:
http://homepage.cem.itesm.mx/lgomez/ingenia/menu.html Hope that helps
Jose
Mexico