USGS Catalog http://geoport.whoi.edu/thredds/bathy_catalog.html

Dataset Size Last Modified
     Folder  Digital Elevation Models   --
         Folder  Global/   --
         Folder  United States/   --
         Folder  Gulf of Maine/   --
         Folder  Other Regional/   --

THREDDS at USGS WHCMSC see Info
Documentation