Within this nice post about different sites and technology to use in the classroom and for workflow is this cool idea:
Students submit their right angled triangles and they’re arranged onto a scaled version of the unit circle (see: all circles ever). Great for discussion and visual prompts.
Pythagorean Proof using tiling of two squares.
Handy. (Pun intended)
Very useful webpage of surd values of a large number of Sine / Cosine angle values. More than the usual five or so.