The river road hamstery site is brilliant:
http://hometown.aol.com/theriverrd/genetics.htm
It has everything from the basics, to more complicated and is the site I have found the most beneficial.
I've looked at loads of others too, but can't remember where at the moment, but will let you know if I remember.
Also the Hamsterlopaedia (book) is meant to be really good, and I will soon be purchasing it myself.