History, Geography, Cartography and Time Keeping

History
Geography
Cartography
Time Keeping

History:

Site:
Comments:
Dendrochronology Dating using tree rings. Also a little about carbon-14 and solar events.
History Hub
"A support community managed by the National Archives for researchers, citizen historians, archival professionals, and open government advocates."
Vintage News
Not exactly what most of us think of as "history", but a lot of good stuff that's old or very old.



Geography:

Site:
Comments:
CIA World Factbook Maps
Wide range of maps kept up-to-date
Geospacial Solutions

Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time. 
Excellent book by Dava Sobel.  Could also belong in Time Keeping. 
World Atlas



Cartography:

Site:
Comments:
Geo Lounge
all things geography
Geokov
   Map Projections - types and distortion patterns  
   Free Educational and Spatial Data Resources   
Online mapping tools.
National Geospacial-Intelligence Agency



Time Keeping:

Site:
Comment:
Computerphile's overview of time zones.
Serious and very funny.
GPS World 
This site could also be in Cartography or Geography.
(The) Greenwich Meridian 
Large site of information including history, calculations and links.
Network Time Protocol
NTP software, Public server pool
Royal Observatory Greenwich 
The historical standard for GMT.  300 foot error.  The actual observatory was closed in 1998.  Deeper explanation with extensive references.
Tycho (U.S. Naval Time Service Department)
Time standards