Reference

general

AllExperts
Ask a Librarian (Library of Congress)
Atlapedia
Bartleby.com
CIA World Factbook
Credo Reference
Encyclopædia Britannica
Encyclopedia.com (Columbia)
Fathom
How Stuff Works
Infoplease.com
Internet Public Library
iTools
People's Network [UK]
Refdesk.com
Resource Central
Where to do Research

standards

Currency Symbols (ISO 4217)
Date & Time Notation
E-mail
Metric Association [US]
Paper Sizes

maps

Bing Maps
Brilliant Maps
British Columbia Maps
Flightradar24
Google Maps
MapQuest
Michelin
National Geographic Maps
Streetmap [UK]
U Texas Library (Perry-Castañeda Collection)
World Atlas
World of Maps

etc.

Area Code Decoder (North America)
Astronomy
Biography
Civil Rights Litigation Clearinghouse (Research Library)
ClimateProgress
Collectors Universe
Day of Birth [UK]
dMarie Time Capsule (what happened when)
Earth & Sky
Emojipedia
Environmental Working Group
Find a Grave
Fish Database
Freedom House (worldwide freedom)
Gaisma (solar times worldwide) [FI]
Gazetteer of British Place Names
Government Data [CA] | [UK] | [US]
Geographic Distance Calculator | + | + | +
GetHuman
Greenwich Mean Time
The Internet Archive | Wayback Machine
Internet FAQ Archives
Knots
Melissa Lookups
Military-Industrial Complex
Name, Behind the (first name etymologies)
Nolo Press (legal information)
Number Gossip (facts about specific numbers)
Philosopedia (philosophy)
PhoneSpell (number mnemonics)
PhysLink.com (physics, astronomy)
Postal Services: [CA|?|$] | [UK|?] | [US|?]
Prelinger Library | Archives
Random Numbers | + | + | +
Royal Observatory Greenwich
Sunrise/Sunset Times
Symbols.com
TerraServer | +
Timeline Archive
Unit Converter | + | + | +
U.S. Patent & Trademark Office
Visible Earth (NASA)
World Clock (standard version)
World Paper Money
World Timezone Map
Zip Code Statistics