I'm currently selling a set of Creative X-540 speakers for $30.

You can see it here: http://www.newegg.com/Product/Product.aspx?Item=N82E16836121006

It's not the greatest set of speakers in terms of sound fidelity, but it does handle 5.1 nicely, the mounting is easy, and it's cheap. I'm selling it because it takes up too much of my desk space, and I realized I don't use them nearly as much as I should. They are about one year old with no physical defects of any kind.