Definition and properties of a cube.
Math Open Reference

Finding the midpoint of a line segment given the coordinates of the endpoints
Math Open Reference

Great (and short)Powerpoint Presentation on Points, Lines, and Planes.
DocStoc

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

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

The site gives a small applet exploring the relationship between circles centered at the origin, linear equations, and pythagorean triples.
Pythagorean Triples

Definition of 'Angle Bisector' and a general discussion of bisection. Link to 'line bisector'
Math Open Reference

This page discusses the different types of lines in geometry, including medians, bisectors, rays and more.
NCTM Illuminations

Definition of collinear points  three or more points that lie in a straight line
Math Open Reference

Definition of a transversal. A line that cuts across two or more (usually parallel) lines. Also perpendicular transversal
Math Open Reference
