As epigene san showed the good website explaining about どどいつ, I'm introducing another website which has a nice collection of どどいつ, some are very old and traditional, others are quite new.
たちはな亭
http://park17.wakwak.com/%7Etatihana/
Not really scientific but here are two nice sites.
漢字のなりたち
Short animation showing how the kanji was made from a picture(?).
篆書でGO!
Introducing some interesting 篆書 an ancient style of kanji which is now mainly used for 印鑑 (seal).
Some of them really look like picture than letters!