We've mentioned it before, but the rarely-updated Rotten Library never gets old. It was the first website that I fell into the click-a-link forever timewaster. The writing is sharp and crisp, the illustrations are nearly perfect, and most of the articles are exactly long enough to fell complete but still want more. Wikipedia has mostly taken the role of time-stealing-clicking now, but Rotten showed me the way.
Some of my favorites:
Everything in Crypotzoology
An extended, elaborate argument that Al Qaeda is connected to the Assassins cult
On the silly Matrix Trilogy
But really, it's all good stuff.