Another important source I use for writing historical fiction is to know when various advances were made in science, mathematics and technology. Good not to use radios before they were invented, or cotton looms before they existed. Even things like light bulbs, electricity and television are harder than you think. Pardon the small print, but these are useful links by topic. Found it on StumbleUpon at the following link, not sure the original source document, probably http://www.3rd1000.com.
http://www.stumbleupon.com/su/2Ka4MI/:m-bt.SFj:WJjdm5D./www.3rd1000.com/chronology/chrono.htm/
The Chronology of Events in Science, Mathematics, and Technology
Chronology of Biology and Organic Chemistry
Chronology of Medicine and Medical Technology
Chronology of General Technology
Chronology of Pure and Applied Mathematics
Chronology of Geology
Chronology of Geography, Meteorology, Paleontology, Science Philosophy and Publishing
Chronology of Agriculture and Food Technology
Chronology of Clothing and Textiles Technology
Chronology of Motor and Engine Technology
Chronology of Transportation Technology
Chronology of Underwater Technology
Chronology of Communication Technology
Chronology of Photography Technology
Chronology of Calculator and Computer Technology
Chronology of Time Measurement Technology
Chronology of Temperature and Pressure Measurement Technology
Chronology of Microscope Technology
Chronology of Low Temperature Technology
Chronology of Rocket and Missile Technology
Chronology of Materials Technology
Chronology of Lighting Technology
Chronology of Classical Mechanics
Chronology of Electromagnetism and Classical Optics
Chronology of Thermodynamics, Statistical Mechanics, and Random Processes
Chronology of States of Matter and Phase Transitions
Chronology of Quantum Mechanics, Molecular, Atomic, Nuclear, and Particle Physics
Chronology of Particle Physics Technology
Chronology of Gravitational Physics and Relativity
Chronology of Black Hole Physics
Chronology of Cosmology
Chronology of Cosmic Microwave Background Astronomy
Chronology of Background Radiation Fields
Chronology of Galaxies, Clusters of Galaxies, and Large Scale Structures
Chronology of Interstellar and Intergalactic Medium
Chronology of White Dwarfs, Neutron Stars, and Supernovae
Chronology of Stellar Astronomy
Chronology of Solar Astronomy
Chronology of Solar System Astronomy
Chronology of Astronomical Maps, Catalogs, and Surveys
Chronology of Telescopes, Observatories, and Observing Technology
Chronology of Artificial Satellites and Space Probes
Michael Bradley - Time Traveler 