Stumbled across this the other day, and while I don’t currently have the need for it (or a copy of ArcGIS to try it out on), it sounds useful enough to post about. NOAA’s Center for Coastal Monitoring and Assessment offers a free extension for ArcGIS called the Habitat Digitizer:
The Habitat Digitizer Extension is designed to use a hierarchical classification scheme to delineate habitats by visually interpreting georeferenced images such as aerial photographs, satellite images, and side scan sonar. The extension allows users to create custom classification schemes and rapidly delineate and attribute polygons, lines, and points using simple menus. The extension allows new hierarchical classification schemes to be easily created, modified, and saved for use on future mapping projects. There are several advantages to using classification schemes with a hierarchical structure including: the detail of habitat categories can be expanded or collapsed to suit user needs, the thematic accuracy of each category/hierarchical level can be determined, and additional categories can be easily added or deleted at any level of the scheme to suit user needs.
While written for habitat digitization, it could prove useful for any digitization projects with extensive classification requirements. Versions are available for ArcView 3.0, ArcGIS 9.0, and ArcGIS 9.2 from the product page; download files include a PDF manual.