http://www.coastal.udel.edu/faculty/rad/linearplot.html water waves
http://www.ngsir.netfirms.com/englishhtm/Interference.htm lots of applets
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html wave demos
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=16 reflection and refraction
http://www.geocities.com/capecanaveral/hall/6645/propagation/propagation.html same as above
http://www.abdn.ac.uk/physics/ntnujava/waterSurface/waterSurface.html another water surface one
http://library.thinkquest.org/19537/java/Wave.html really nice sound wave
http://illuminations.nctm.org/tools/soundwave/ excessively cool sound wave
http://www.udel.edu/idsardi/sinewave/sinewave.html simply about waveforms
http://www.kettering.edu/~drussell/demos.html numerous wave demos really good
http://www.physics.smu.edu/~olness/www/05fall1320/applet/pipe-waves.html standing waves in a pipe
http://pdgusers.lbl.gov/~aerzber/aps_waves.html guide to lots of applets
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/index.html lots of great simple stuff