Looking back on the courses, units, and concepts/skills I have taught, I think right-triangle trigonometry must be the topic I have taught most often.
Five years ago, I student taught for several months in a western Massachusetts high school. The first unit I was given to prepare/teach/assess/grade by myself (instead of just doing one or two of these tasks, assisting and learning from the teacher) was a month-long Trigonometry unit in a Geometry class. I prepared this page of notes (scribd, html) back then, which I still use with my students today.
In every year of my teaching career save the first, I have taught trigonometry of the right triangle, often in more than one course each year! I have taught it in Geometry, and in Algebra II with Trigonometry (wherein many students have forgotten much of what they learned in Geometry, even if I was their teacher for both classes :-[
Most recently–spring semester and now again for the fall semester of 2009–I have been teaching right triangle trigonometry and its applications to vector analysis of forces on truss bridges & other structures, in an introductory engineering course. One difficulty is that I am teaching it to these students usually for the first time, before they encounter trigonometry in Geometry or another math class. My introductory engineering students are mainly ninth and tenth graders. Also, applying trigonometry to vectors and trusses requires additional mathematical sophistication. And so, even though I have taught trigonometry to more than ten classes in the past, I find these students struggling.
Therefore, I ask: Does anyone know any good online resources about trigonometry that I could use with / share with my students? Or have any suggestions for making right triangle trigonometry more motivating and memorable?