Certainly, one of the most important things that a SDI organization can help the trained professional, policy makers, industry, and the lay public is to find data for their needs -- data that covers their area of interest, in the timeframe needed, with the right scale and resolution, and related requirements.  The FGDC provides such a service often called ‘data discovery’.

The Federal Geographic Data Committee (FGDC) provides a listing of registered clearinghouse nodes both domestically and globally.  The list provides metadata describing the actual data held by the data steward, provides the URL of the site and some of their operational characteristics.  The sites are all queried hourly and the user can see if a site is currently up and responding, or has timed out, or is down.  You can search for international data and services using the Global Spatial Infrastructure Gateway.