The USDA Aerial Photography Field Office (APFO) recently announced that they are now publicly distributing the 4-band NAIP imagery in addition to the natural color imagery. To access this data, use the following URL in ArcGIS Desktop: http://gis.apfo.usda.gov/arcgis/services. More detailed instructions can be found on the APFO website at:http://www.fsa.usda.gov/Internet/FSA_File/2013_apfo_webservice_10x.pdf. Developers or ArcGIS Online users will want to include "rest" in the link in order to identify service "endpoints": http://gis.apfo.usda.gov/arcgis/rest/services.
Minnesotans can thank Bill Burgess with the National States Geographic Information Council (NSGIC) for the tip.