Khan Academy
Khan Academy: Solving for a Side in Right Triangles With Trigonometry
Learn how to use trig functions to find an unknown side length in a right triangle.
Other
Dans Math: Lessons: Trigonometry
College professor Dan Bach reviews basic trig concepts, including trig functions, right triangles, circles, radians, and polar coordinates. Site includes animated graphs and detailed examples.
Other
Trig Without Tears: Solving Triangles
This page provides a good explanation of how to solve oblique triangles (triangles containing no right angles.) The Law of Cosines section is about halfway of the way down the page.
Khan Academy
Khan Academy: Intro to Inverse Trig Functions
Learn about arcsine, arccosine, and arctangent, and how they can be used to solve for a missing angle in right triangles.
CK-12 Foundation
Ck 12: Trigonometry: Law of Sines
[Free Registration/Login may be required to access all resource tools.] Learn how to use the Law of Sines with different types of triangles.