GoNoOdle is a must-check-out-because-your-students-will-love-it website. It is ideal for the primary grades where students' stamina is limited to small burst of time. You can create an account for free and then access any number of brain break videos/exercises. Olympians will take your students through short training sessions before leading them in a virtual athletic competition. It is a great way to give your students a short break to get out the wiggles in the classroom before transitioning into a lesson.
For other virtual tools, check out my pinterest board of "websites useful to teachers."