Brick Fetish - great source for history, catalogues, etc...
G. Istok's page on LEGO (try the links at the bottom)
Arnoud's pages on old LEGO with lots of useful information (in Dutch)
Pages of Karl-Heinz on brick types, logos, window evolution, trees and other useful stuff (in German)
LEGO car miniatures and some late 50's sets & leaflets