Here are some links on Calvin & Hobbes that I've looked at for you. I know there are many others, but I've just put the ones I've checked...

First of all the sites in english :
The Calvin & Hobbes Gallery
Calvin and Hobbes' Jumpstation (at least a hundred links !)
Calvin Is God
Calvin and Hobbes' suburban jungle
It's a Magical World
Calvin and Hobbes collectibles
The official site spescially for its daily strip.

Then some sites in french :
La page de Calvin et Hobbes.
Baloo's page sur Calvin & Hobbes