Great description on what points, lines, and angles are.
SparkNotes

A helpful scientific calculator that runs in your web browser window.
Holt Online Learning

Similar triangles  all three corresponding angles the same. AAA
Math Open Reference

A quick way to test your knowledge of angle types
Math Open Reference

Discussion of the way angles are measured in degrees, minutes, seconds.
Math Open Reference

Coplanar objects are those lying in the same plane
Math Open Reference

Definition and properties of adjacent angles  those that share a common leg or ray
Math Open Reference

Definition of an angle.
Math Open Reference

This website is a worksheet to estimate and measure angles. The answer sheet is there also.
MathDrills.com

Explanation and examples of angles along a straight line.
Math is Fun
