Federal Business Opportunities (fedbizopps) - Electronic Posting System - allows industry to search for government acquisition opportunities and serves government buyers by providing the capability to post solicitations on the internet.

Grants.gov – Search for Grants

Federal Procurement Data System - the official statistical data base on procurement contract transactions.

Department of Agriculture 
USDA Procurement
USDA Points of Contact and Business Opportunities Information
Agricultural Research Service
Farm Service Agency
Rural Business-Cooperative Service

Department of Commerce 
Office Acquisition Management and Financial Assistance
Office of Small and Disadvantaged Business Utilization (OSDBU)

Census Bureau 
Acquisition Management

National Institute of Standards and Technology (NIST) 
Contracts Office

National Oceanic and Atmospheric Administration (NOAA) 
Acquisition Divisions
Grants Office
Western Administrative Support Center

Patent and Trademark Office 
Patent and Trademark Office Acquisitions

Department of Defense
Business Opportunities
Missile Defense Agency - Doing Business
Defense Acquisition Information
Defense Advanced Research Projects
Defense Information Systems Agency
Defense Intelligence Agency
Doing Business with Defense
National Imagery and Mapping Agency - Select Business Opportunities Link
Office of the Under Secretary of Defense for Acquisition and Technology
Defense Procurement and Acquisition Policy
Small Business Innovation Research (SBIR) Program
Tri-Service Contract Solicitation Network (Army Corps of Engineers, Naval Facilities, etc.)

Defense Logistics Agency
Doing Business with DLA and other DLA Sites
DCMC - Defense Contract Management Command 
DESC - Defense Energy Support Center
DSCC - Defense Supply Center Columbus
DSCP - Defense Supply Center Philadelphia 
DSCR - Defense Supply Center Richmond

US Air Force 
Acquisition Home Page
Air Force Contracting - Business Center

US Army
Army Business Acquisition Website
AMC - Army Materiel Command Business Opportunities
Acquisition Policy
RDECOM - Research, Development, and Engineering Center, Acquisition Center
AMCOM - Aviation & Missile Command - Redstone Arsenal

ARL - Army Research Laboratory 
ARL/RDECOMAC Adelphi Contracting Opportunities
Doing Business with ARL
CECOM - Communications-Electronics Command
FORSCOM - Forces Command

RDECOM - Research, Development, and Engineering Command 
Business Opportunities
Acquisition Center 
JPEO-CBD Joint Program Executive Office for Chemical Biological Defense

US Navy 
Acquisition & Business Management Online
NECO - Navy Electronic Commerce Online 
MARCORSYSCOM - Marine Corps Logistics 
MSC - Military Sealift Command 
NAWCTSD - Naval Air Warfare Center Training Systems Division - Orlando
NAVAIR - Naval Air Systems Command Business Opportunities
NAVFAC - Naval Facilities Engineering Command Contracts Support
NAVICP - Naval Inventory Control Point
NAVSUP - Naval Supply Systems Command 
ONR - Office of Naval Research
NRL - Naval Research Lab
SPAWAR - Space & Naval Warfare System Command
Systems Center San Diego

Department of Education
Grants and Contracts

Department of Energy 
Office of Procurement
Business Opportunities

Department of Health and Human Services 
Office of Acquisition Management 
Grants & Funding

National Institutes of Health 
Grants and Funding Opportunities

Department of Housing and Urban Development 
Contracting at HUD
Guide to Contracting with HUD

Department of the Interior 
Acquisition, Financial Assistance, and Property Management
Bureau and Office Acquisition Pages
IDEAS Electronic Commerce

Department of Justice 
Procurement Opportunities
Doing Business with DOJ

Department of Labor 
Grant and Contract Information

Department of State 
Acquisition Web
Contracting Opportunities
Business Opportunities

Department of Transportation 
Acquisition and Grants Home Page
Acquisition Sites
Contracting Opportunities
Doing Business With The Department of Transportation
Office of Small and Disadvantaged Business Utilization (OSDBU)

Federal Aviation Administration 
FAA Acquisition Tool Set (FAST)

Department of Treasury 
How to Do Business with Treasury
Office of Small and Disadvantaged Business Utilization
Bureau of Engraving and Printing 
Customs Service
Financial Management Service
Internal Revenue Service
Secret Service

Department of Veterans Affairs 
Office of Acquisitions - Business Opportunities
Office of Small and Disadvantaged Business Utilization

Consumer Product Safety Commission 
Business Information

Government Printing Office 
Procurement Services

Environmental Protection Agency 
Contracting with EPA
Grants
National Center for Environmental Research - Grants

Federal Communications Commission 
Office of Communications

General Services Administration (GSA) 
Selling to GSA

National Aeronautics and Space Administration 
Office of Procurement
NASA Acquisition Internet Service
Center Procurement Sites
NASA Business Opportunities
Federal Business Opportunities
E-mail Notification of Opportunities
Office of Small and Disadvantaged Business Utilization (OSDBU)
Small Business Innovation Research (SBIR) Program & and Small Business Technology Transfer

National Science Foundation 
Grants Contracts

National Transportation Safety Board 
Acquisition

Nuclear Regulatory Commission 
Contracting

Office of Personnel Management - has developed and maintains a document that includes all of the authorities available to all Federal agencies and how they can be used to manage the challenges that all agencies face when attempting to recruit and retain a highly qualified workforce. The document is written in plain English: Human Resources Flexibilities and Authorities in the Federal Government

Social Security Administration 
Office of Acquisition and Grants

U.S. Agency for International Development (USAID) 
Business Opportunities

U.S. Postal Service 
Doing Business with the U.S. Postal Service