The derivative
Animations and movies
Movie: That's calculus, Episodes 4 and 5. In Josh and the Mathemagician, Josh looks at maxima and minima problems and derives some rules for derivatives. [Josn Kornbluth]
Animation: Secants on a parabola approaching a tangential limit. [Lane Vosbury]
Animation: Secants on a parabola approaching a tangential limit -- with numerical data. [Douglas Arnold]
Animation: The same animation, but with the tangent line included for comparison. [Douglas Arnold]
Animation: Another animation showing the secant converging to the tangent, but this time with the f(x+h)-f(x) and h pieces shown specifically. [Lesley Robinson]
Animation: Secants approaching a cusp, a type of non-differentiable point.
Animation: Secants passing through a vertical tangent, another type of non-differentiable point. [Douglas Arnold]
Animation: The tangent line moving along a curve. [Paul Garrtet]
Animation: The tangent line moving along a curve. [Lane Vosbury]
Animation: The tangent and normal lines moving along a curve. [Lane Vosbury]
Applets
Calculus animations applet: An interactive animation of secant lines approaching a tangent line, with lots of numerical features and a choice of functions. [Monte Vista BC calculus]
Secant-tangent applet: A pair of applets which show both secant approximation of tangent lines and various "good" and "bad" tangents. [Hobart and William Smith Colleges]
A secant to tangent applet: Plot any function you like, and observe how the slope of the secant line (in green) can be used to approximate the tangent slope at a point (in red). [David Eck]
Graphing the tangent line: Plot any function you like, and see the tangent line at any specified point. [Vanderbilt toolbox]
First derivatives applet: Plot any function you like, and see the graph of it's derivative next to it. Move the slider around to see how the slope of the tangent line to the graph of f affects the moving point on the graph of f'. [David Eck]
Derivatives applet: A more "portable" pair of applets which do the same thing. [Hobart and William Smith Colleges]
Differentiation 1 page: Several applets which test your understanding of the derivative, including matching tests and animations. [Maths online]
Online problems
Problems: Test your understanding of the concepts of the derivative with this interactive test. [Maths online]
Problems: Match the graph of a function to the graph of its derivative. [Maths online]
Problems: Calculate the derivative from the definition. [Visual calculus]