Laplace transforms

Interactive mathematics site which has explanations and then questions, with worked examples

http://www.intmath.com/Laplace-transformation/Intro.php

Laplace transformations quiz (but no worked answers)

http://www.ee.adfa.edu.au/staff/hrp/Quiz/control/L1-quiz.html

ODE’s

Phase Portraits for ODE’s and Autonomous systems with ability to input systems

http://www.math.psu.edu/melvin/phase/newphase.html

Fourier series and transforms

Explanation and worked examples of Fourier series representations, with moving diagrams showing how it estimates a line of best fit over a function: http://www.sosmath.com/fourier/fourier1/fourier1.html

An application that helps to explain a practical use of Fourier series representations

http://www.falstad.com/fourier/