This year, I'm teaching pre-calculus for the first time, and I'm taking full advantage of being able to teach trigonometry as deep as possible. We're spending the entire second half of the course on it, and so far after about 4 weeks, my students have still not picked up a calculator, and they know an tremendous amount of material. They are getting a great depth of knowledge on this topic, and they are making all of the connections without any kind of calculating device whatsoever. To me, that is awesome. Not only do they know the unit circle inside and out, but they are also beginning to estimate values of the trig functions as well.
Our ultimate goal was to learn the diagram above, which has been achieved. This diagram gives a beautiful illustration of where the names 'sine,' 'cosine,' and 'tangent' come from, a great visualization of where the trig functions fall within the unit circle, and a natural derivation of the Pythagorean Identities. If students can learn this diagram and understand what it means, they have gained a ton of knowledge that I'm willing to bet is not necessarily taught in the average trig class. I have not seen this in any text book (unfortunately, most text books don't seem to focus on the unit circle, which I don't understand), maybe this is above high school level, but I do believe it is ridiculously valuable.
Our next step is to use it to graph each of the trig functions. A colleague of mine has created a Sketchpad file where the coordinate rotates around the unit circle and all six graphs are created simultaneously. It's a little overwhelming, but captivating and artistic at the same time. When he showed it to his class, they were able to match each function with the appropriate graph, and they now understand why the graphs look the way they do. They were also able to explore the relationships between each of the graphs, why the asymptotes exist, and so much more.
I'm not sure if the half-angle and double-angle properties are in there (I haven't investigated that quite yet), but I'm hoping I can come up with something.
All in all, this diagram excites me. It makes sense, and it allows students to have fun with numbers and they don't question it. I have not had a single student refuse to do any of this work. They see the connections, they appreciate the math that we are doing, and they understand how much smarter they are now.