On the web
There are several websites that have exercise and stretching demonstrations. These are helpful not just for learning the exercises, but also for becoming aware of new exercises to spice up your routine, and also to review your form from time to time. Here I list more than one website, as they vary in content. As well it is often helpful to see demonstrations from different points of view. A few sites with quality content:
For stretching exercises, I recommend the ExRx muscle directory found here. They also have exercise demonstrations, but sometimes the demonstrations use poor form. If you click on a body part, you will see stretches for it listed in the right hand column.
for its indepth explanations of how to squat, deadlift and bench press properly.