Solar radiation
Clear sky calculator for pyranometers
Simple pyranometer (David Brooks)

Geographic Information Systems (GIS)
Quantum GIS Wiki
Ordnance Survey Data Hub
ONS Open Geography Portal
Digimap

Electronics
SparkFun Eagle tutorial

Computing
Virtual Network Computing (TightVNC)

RTL Sofware Defined Radio (SDR)
APT reception
SpectrumLab Users Group

Photographic Light Meters
James Ollinger’s excellent website
Weston Light Meters
History of the Weston company
The measurement of light in photography

General interest
Atmospheric Optics
Space Weather
Space Environment Centre