The Library of Congress is one among many organizations putting music archives together.
The fruit of their efforts can be viewed here. Performing Arts Encyclopedia
The New York Public Library for the Performing Arts is home to a wide array of circulating and non-circulating media. This includes music, of course. Their Song Index allows users to search for songs in their collection through a variety of means.
The ARChive of Contemporary Music is a music library, archive and research center here in New York City. Their collection consists of popular
music of all cultures and races throughout the world from 1950 to the
present. Quite an undertaking! Check out the ARChive