Finance and Government Search Engines

Bankrate.com — Database of interest rates for different loan types, mortgages, and savings accounts.
InvestIQ — Market data from around the world in regions.
BigCharts — Quotes and performance charts on different stocks and mutual funds.
SmartMoney.com Tools — A portal of for stock analysis tools.
NASDAQ Trader — A database of stock data from the NASDAQ stock exchange.
SEC Info — EDGAR and SEC filings searchable by name, industry, SIC code, etc.
EDGAR Online — SEC filings searchable by ticker or company name.

Government Search Engines

Copyright Records (LOCIS) — Online copyright records, documents, serials, and multimedia.
American FactFinder — Aggregate census bureau data to be searched by city, county, or ZIP code.
FedStats — Gateway for statistics on 100 US federal agencies.
United States Patent and Trademark Office — Database of patents,  full-text and full-page images.
Historical Census Browser — Repository of historical US census data. Going back to 1790 compiled by the University of Virginia.
Geospatial One Stop — Awesome GIS data warehouse of geographic data, shapefiles, imagery, and displayable on maps.
Grants.gov — Grant opportunities, from everything under the sun.
Technology Opportunities Program Grants Database — Listing of technology grants, peruse by keyword, state, and year.
United States Government Printing Office (GPO) — I mentioned this earlier, they seem to have everything. A search engine for mutliple government databases: US budgets, campaign reform hearings, code of federal regulations, congressional bills, etc
CIA Electronic Reading Room — The usual uninteresting declassified CIA documents.
POW/MIA Databases and Documents — Info on POWs and MIAs.
ZIP+4 Lookup — US ZIP codes and ZIP+4 codes

Economic and Job Search Engines

EUROPA Press Release Database — Database of press releases by the European Union.
FreeLunch.com —Directory of free economic data.
Bureau of Labor Statistics — Job-based and consumer economic info from the US Department of Labor.
Salary Wizard Calculator — Tools that shows national average salaries adjusted by location for different jobs.
Economagic — A data directory containing over 200,000 econ files.
Penn World Tables — National income data for all countries for the years 1950-2007.
America’s Job Bank — Database of jobs and resumes.
USAJOBS — Portal of data on federal government jobs.
Regional Economic Conditions (RECON) — Economic data available by state, county, and MSA.