Literally thousands of pages of muscles and exercises. I use this site all the time - and as a trainer you will too! Oh yeah - it's Free!

This site started as a project by a college student - and has grown to a very comprehensive resource for all fitness professionals.

Look up each muscle and view online video clips of each exercise which works those muscle groups. Many of the exercises are somewhat basic - but you'll still find yourself spending hours looking through this site:

http://www.exrx.net/Lists/Directory.html