GoSwim.tv featuring Steve Haufler...it is a great video filled with great tools, methods, and progressions. I plan to review the DVD soon, but in the mean time I want to write about one of the tools Steve Haufler uses regularly throughout the video; mirrors.
Finis Inc manufactures mirrors for placement on the bottom of the pool while working on swimming skills. The 45.5"x28" polished aluminium mirror weighs about 3 pounds and is easy to place on the bottom of the pool so your swimmers can see themselves as they pass or hover over it.
I have been using the mirrors to encourage my learn to swim students to do anything from put their faces in the water, to working on proper stroke technique and body position during freestyle and breaststroke. If you put several mirrors in a line, they would be appropriate for more advanced swimmers as they work on hand placements, etc.
The mirrors themselves are pretty sturdy when in the water and in the bottom. Having said that, you want to be careful when putting them in the water and taking them out. Aluminum can bend, bow, and be dented easily. Small dings won't make much of a difference, but avoid dropping or banging the mirrors about.
Finis sells the mirrors for around $105, but you can find them for around $10-$15 cheaper at amazon.com. All in all, a pretty good investment for swimmers and learn to swim students. Definitely worth the small investment.