USDA Web Sites:

ARS, Urbana, Illinois
ARS National web site

Other US Government Sites of Interest:

The PLANTS database is a single source of standardized information about plants. This database focuses on vascular plants, mosses, liverworts, hornworts, and lichens of the U.S. and its territories. The PLANTS Database includes names, checklists, automated tools, identification information, species abstracts, distributional data, crop information, plant symbols, plant growth data, plant materials information, plant links, references, and other plant information.
Job openings in the federal government are listed.
The buck stops here.

Non-Government Links:

National Soybean Research Lab
American Society for Microbiology
Weed Science Society of America

University of Illinois at Urbana-Champaign:

College of Agricultural, Consumer and Environmental Sciences (ACES)

Department of Natural Resources and Environmental Science