As an ELS teacher I am always looking for authentic uses of English for my students to listen to. The great thing about Randall's ELS lab is that it has a huge collection of just such audio. It would impossible for my students to get enough listening time from just me.
Randall's gives me a resource to send my student to get supplemental listening practice with a great set of built in evaluation tools. Lessons are clearly cataloged by content and difficulty level making it easy to find appropriate lessons. It's a great website and one I will be using a lot in the future.