This website is a short introduction to Trigonometry by a professor at Clark University. It is very easy to follow, is full of animations and study problems for the reader to work through.

Excerpts from site:

Trigonometry for you
Trigonometry is useful. If you would like to learn a bit about trigonometry, or brush up on it, then read on. These notes are more of an introduction and guide than a full course. For a full course you should take a class or at least read a book.

There are no grades and no tests for you to take, and no transcripts and no awards. There are a few exercises for you to work on, but only a few. The exercises are the most important aspect of a trigonometry course, or any course in mathematics for that matter.
Your background
You should already be familiar with algebra and geometry before learning trigonometry. From algebra, you should be comfortable with manipulating algebraic expressions and solving equations. From geometry, you should know about similar triangles, the Pythagorean theorem, and a few other things, but not a great deal.
How to learn trigonometry
Trigonometry is like other mathematics. Take your time. Write things down. Draw figures.

Work out the exercises. There aren't many, so do them all. There are hints if you need them. There are short answers given, too, so you can check to see that you did it right. But remember, the answers are not the goal of doing the exercises. The reason you're doing the exercises is to learn trigonometry. Knowing how to get the answer is your goal.