Comfortable Low Energy ARchitecture
Color Science
Repository of Colo(u)r related info
Light Measurement Handbook
Introduction to photometric measurements
The Joy of Visual Perception: A Web Book
A bit outdated, but still a nice reference on human vision.
Energy Design Resources
Guide to energy efficient design practices
Passive solar design using computer generated sun charts
Does exactly what it says on the tin.
The ImageFactory
Stereoscopic images for visualisation of cultural heritage; Good introduction to stereoscopy.