Purple Math
Purplemath: Angles of Inclination and Declination
Explains the terminology for angles of elevation, depression, inclination, and declination. Demonstrates how to 'translate' exercises into triangles and equations.
Clark University
Clark University: Dave's Short Trig Course: Tangents and Slopes
Explains what "tangent" is and its role in the right triangle. Slope of a line is investigated and tangent for special common angles is given. Angle of elevation and angle of depression are also covered here.