The Library of Congress has opened a new site -- http://id.loc.gov -- which will provide access to various vocabularies and standards maintained at LC. This replaces lcsh.info which was on a non-official site and provided access to LCSH is machine-readable formats. Below is the announcement message sent out by Sally McCallum, head of the Network Development and MARC Standards Office.
 

Watch for the balloons! This site launches officially on November 19th. We expect to have more than 200 vocabulary listings in our directory by then, and hope that a number of them come from outside the "development circle".
We'd like users and visitors to feel comfortable adding content themselves - comments and blog entries, and whitepapers and favorite links to resources they've found valuable. We hope this will be an outstanding resource for builders of controlled vocabularies and for the wider content and knowledge management community as well.