NationMaster -- aggregates statistics from many web sources; single best source of statistics on any country.
StateMaster -- aggregates statistics from all US States.
Agency Compile -- best free source of public relations and advertising agency information on the web; searchable by client, geography, firm, etc.
GuideStar -- best free online source of informaton on non-profits; search the company name; includes IRS 990 reports.
Data.gov -- Best single location for most government statistics; aggregates at the location level, not the spreadsheet level, in most cases.
CIA World Factbook -- Provides background, data and demographics for nearly any country.