J. Talbot and Y.P. Varshni, University of Ottawa.

http://www.achilles.net/~jtalbot
/data/elements/index.html

This page and JAVA applet from the Laser Stars site shows the line emission spectra of the light elements in gas discharge tubes.

Physics 2000 Initiative, University of Colorado at Boulder.

http://www.colorado.edu/physics/
PhysicsInitiative/Physics2000/
quantumzone/index.html

This lavishly illustrated and JAVA-rich (and often slow) site includes a detailed storyline describing the spectral lines, the Bohr atom and related topics. In particular, check out the animations that show the creation of X-Rays via Bremsstrahlung and K-shell knockout.

J. Talbot's Laser Stars, University of Ottawa.

http://www.achilles.net/
~jtalbot/history/

This collection of pages presents the history and operation of lasers as an adjunct to the study of natural laser phenomena in stars. There are also links to laser use in Holography at the bottom of the page.

http://www.periodic.lanl.gov/

A sophisticated online periodic table of the elements created by the Los Alamos Nuclear Laboratory.

Radiology Centennial Inc., Penn State University Department of Radiology.

http://www.xray.hmc.psu.edu/rci/centennial.html

One of the best of a number of sites celebrating the 100th anniversary of the discovery of the X-ray by Rontgen in 1895. This site describes the history and theory of X-rays, and discusses medical applications of X-rays at length.