Site with lots of simple interactives from a variety of subject areas. Science and Math interactives are mostly for secondary students, but some Language Arts and History interactives are for younger students. These would be good for introductions to a unit/lesson or serve as a simple diognostic or review to check for understanding midway through a lesson.
Science based Voicethreads that follow the R.A.F.T. model of science writing. Learners choose a "Role", and then write for a particular audience with a given format and topic. This is a great example of giving students some choice, while still managing to having them write within a given topic and for a purpose.