Plyo exercises are like general strength exercises…they are limited only by your imagination. The means and methods are really dependent on what you're trying to accomplish with the exercise. For sprinting, jumping with a vertical emphasis (as opposed to horizontal) seem to have the greatest impact on top-end sprint speed performance.
Depth jumps are jumps where you fall from a height before rebounding in to a jump. I recently wrote a blog entry about depth jumps that you may want to read.
April my article for elitetrack will be up…should be great as I interview WR and WR coaches.