Color spectra of elements undergoing electrical discharge excitation.
This Java program reads a file containing a list of emission line wavelengths and their corresponding strengths then simulates the appearance of the spectrum in a good visual spectroscope (Great visual representation but slow)

Absorption and emission spectrums of many elements
This Java program reads a file containing a list of emission and absorption line wavelengths.(Great site to show that what a element emits it absorbs)

The Frank-Hertz Experiment

When electrons are shot into a vacuum tube with mercury vapour with increasing energies, all of a sudden certain energies are absorbed. James Franck and Gutav Hertz suggested that this was due to electrons around the atom having specific "stable states" or "stationary states" supporting the Quantum Theory.