The unexamined stroke is not worth swimming:

I rebuilt my stroke after reading an article by Terry Laughlin and then attending a Total Immersion workshop.

Be aware of stroke techniques that may lead to Swimmer's Shoulder.

Stroke Monitor

I have also found these Total Immersion videos to be helpful.

Positive Drive Fins

Swedish Goggles

FistGloves

Coach Cecil Colwin offers swimming insights in both of these books.

Coach Ernest Maglischo has released  Swimming Fastest, the third in his series of thorough examinations of the sport.