Here are some great links that I came across, and specifically why I liked them. Please feel free to recommend other sites to me. contact me.
http://www.et.byu.edu/~wheeler/benchtop/gallery.php Amazing high speed video (slowed down) of water rocket launches! Elsewhere on the site, great tips for getting useful video of launches, quirky ideas like putting a water balloon inside the bottle and some thrust curve math.
http://home.people.net.au/~aircommand/index.htm When you're ready for advanced water rocketry, this is the place to go. Sending video camperas up in rockets, splicing bottles together, great video instructions...it's all here;
http://waterocket.explorer.free.fr/index.html The Water Rocket Explorer site shows what happens when an engineer and his sons encounter water rockets. Not only is there is lots of practical information for building simple to complex (parachute) rockets, but also facinating tangential stuff like the section on rockets reaching escape velocity from the Earth. Truly inspired and high quality. And don't miss the research page http://waterocket.explorer.free.fr/research.htm which has slow-motion video clips, pressure/volume curves and links to useful data.
http://homepage.ntlworld.com/telescope/Rocketweb/Launcher.htm Jay Morgan, Cubmaster of Pack 327 (Texas) alerted me to this free-thinking European site. I believe the person running it is James Hardy, but I have not been able to find any contact information. Instead of making a bump in the PVC pipe to make the pressure seal, he wraps PTFE tape (Teflon thread-seal tape)--not so it forms a big bump to jam the bottle against, but rather enough so the bottle neck fits fully over the tape. So you don't have to be quite so precise about where the bottle is on the pipe. However, I am getting some feedback that the Teflon tape rips after one or two launches. Also on this site, a "spring"--just a section of plastic bottle--that pushes up a little on the trigger collar. So it does not depend just on friction to keep from launching. It's a great idea which I will incorproate onto my design. Also instructions for sending up a tiny video camera, and resultant airial videos.
http://www.ast.leeds.ac.uk/~knapp/rockets/ The Univeristy of Leeds Water Rocket page has the most amazing images, both still and video. You can see the still pictures by scrolling down the home page. Click "Slow motion movies" or
http://www.ast.leeds.ac.uk/~knapp/rockets/rocketmovies.html to see these amazing sequences (also seen on the waterrocketexplorer site). Also check out the "Quick Time Movie of the first manned water rocket launch" or
http://www.ast.leeds.ac.uk/~knapp/rockets/1.mov Thanks to Dr. Johannes Knapp of Leeds U.
http://ourworld.compuserve.com/homepages/pagrosse/h2oRocketIndex.htm The Water Rocket Index is a serious site by Paul Grosse that has everything up to and including recovery systems and aerial photography. Wow!
http://hazchem.smoke.com.au/~ic/water-rocket.html This is Ian Clark's water rocket site. Ian is the one who came up with idea of using cable ties to make a release mechanism.
The Wikipedia "water rocket" entry is very interesting. http://en.wikipedia.org/wiki/Water_rocket
http://www.geocities.com/rocketroos/ You can tell by the name (...roos) they're from Australia. With Coke can rockets and multiple rockets, they are definately thinking "outside the box."