This is not something you need every day, but if your CD/DVD player seems flaky, it just might be simply dust on the lens.  If you look at this cleaner, it's basically a blank CD with a number of very gentle brushes attached to it.  Just inserting it briefly (the players often self-eject it after 10-20 seconds) should take care of any foreign objects.  If this fixes a player for you even once, it's probably worth the purchase price right there.