The Fundamental Theorem of Calculus
Animation
Animation: The Fundamental Theorem in effect. [Visual calculus]
Applet
Cumulative area: Look at the "area-so-far" function and see how it's derivative gives you back the original function. [Dan Sloughter]
Antidifferentiation: Calculates the general antiderivative of the given function. [Vanderbilt toolbox]
The Integrator: An online version of Mathematica's powerful symbolic integration program. [Wolfram]
Online problems
Problems: Fundamental Theorem of Calculus. Includes solutions. [Visual calculus]
Problems: Online quiz using the FTC. Includes solutions. [Visual calculus]