A picture or video is randomly shown or can be searched for and the viewer can pose problems and ask questions. After asking your own question, you can check to see what others have asked. Good site to engage students in mathematics.
This website is an incredible collection of applet type things that gets students to interact. I've used it mostly with statistics (coin flipping, dice, spinners, etc.) and geometry. The students can discover things for themselves.
A youtube contributor that discusses various math topics in a fun and new way. Designed to be watched by people of all skill levels it brings new questions and viewpoints to seemingly familiar topics.