Here are a variety of tools that we have found useful in watershed delineation.

The Standards  - http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/

StreamStats - StreamStats is a map-based Web application that makes it easy for users to obtain streamflow statistics, basin characteristics, and other information for user-selected USGS data-collection stations and ungaged sites of interest.  This application is located at http://water.usgs.gov/osw/streamstats/index.html.

ArcHydro Data Model Download- www.esri.com/software/arcgisdatamodels

NED data - National Elevation Dataset (NED) data is available in the NED directory via USGS Seamless site, located at http://ned.usgs.gov/

DRG - Digital Raster Graphics are available at Inside Idaho

24k hydro - 24k hydro is available by quad at the Idaho Department of Lands.   High resolution National Hydrography Dataset (NHD) data is available for most of the state and may be downloaded from the NHD website, located at http://nhd.usgs.gov/data.html.