Data.gov is the one stop website to find and download free government data in raw, structured formats. Federal agencies are proactively posting data on data.gov, including data that is the subject of frequent FOIA requests.
Federalregister.gov is the daily gazette of government. The Federal Register contains information about new and pending rulemakings and other activities of the executive branch. It is fully searchable.
Grants.gov is the place to look for grant opportunities.
Regulations.gov is the place to look for and comment on regulatory rulemakings.
Fedbizopps.gov is the place to find out about opportunities to do business with the federal government.
USAJobs.gov is the place to find out about employment with the federal government.
USA.gov is the US Government portal. It can help you navigate around the Federal government.