These are interesting websites, great for whole-class use for those unexpected 5 minute slots you need to fill. Here's hoping there's at least one you have not seen before.
In no particular order:
1 - Barry Martin's Hopalong Visualiser
Create a vortex journey to travel to a new world. Great for those moments when you need your class wound up a bit more. Move the mouse/press on the screen to change direction.
2 - Rainyday Screen
Fool your class into thinking it is raining inside your classroom. That's it.
3 - incredibox.com
Create some cool jams by clicking on individual characters to make them play a certain part of a song loop. Choose from Beats, Effects, Melodies and Voices. A minimum of 10 recorded loops is required to save and share/download a composition.
A classic game (well, I think I've seen it before) - divide your class into two teams and let battle commence. Or something like that.
In fact, one of the above sites does not rely on any interaction at all. But still looks pretty cool!