Discovery Education
Discovery Education: Web Math: Plots and Geometry
This site provides descriptions and helpful hints regarding conic sections - circles, parabolas, ellipses, and hyperbolas. Content also includes interactive problem solvers complete with a full analysis of the math behind the answer.
Math Open Reference
Math Open Reference: Graphical Function Explorer (Gfe)
This resource provides a free function grapher. Enter up to 3 equations and plot them. Similar to a graphing calculator.