Paul Nylander's Science and Art page
This page features stunning visualizations of physical and mathematical problems.

Math Physics and Engineering applets by Paul Falstad
A load of amazing java applets illustrating physical and mathematical problems.

Bad Astronomy blog by Phil Plait
The author of "Bad Astronomy" and "Death from the skies". Time magazine picked it as one of the 25 best blogs of 2009. I have nothing to add...

Bri's world
A good friend of mine, author of the AVR8 Burn-O-Mat. His page feature board layouts for electrical engineering stuff such as a programmable chain of lights