I took a chance on these Koss earbuds after reading a few reviews and have been pleasantly surprised by them.  The cushion-y part that goes into your ear acts like foam earplugs (which I use often, so I'm comfortable with them).  You give them a squeeze and they'll expand in your ear, blocking out some outside noise.  So, no, they don't 'cancel' sound, but they do suppress a lot of it, even with the player off.  And they come with a replacement set of the foam inserts for when the first pair gets icky or worn out.

The sound is really quite good for a cheap pair of earbuds, particularly the bass. ...