See
ASCAP: New Media/Internet for just about anything you might want to know about music licensin' for internet use.
As mentioned there, if only a single work, or just a few works, are to be featured, on a non-revenue generatin' website, and the works themselves are embedded and not individually downloadable or otherwise accessible-on-demand apart from the piece in which they are embedded, it usually will be cheaper to arrange with the publisher of the musical work(s) for a single-site limited license for just the pertinent works. In some cases, however, the publisher will not provide limited or restricted licenses, leavin' an annual ASCAP license the only practical alternative. ASCAP licenses start at a bit under $300/yr and cover almost all commercially available, published music.