FunkAndJazz has a great collection of SF graff on his flickr acct and I especially liked his hefty amount of tagged door pics. I have a thing about the chaos, competing handstyles and colours that build up over time on doors and find them to be a beautiful sight to behold.
And before the samaritans start asking me the classic question, "How would you like it if your front door looked like that?" Well, the answer is, my door does look like that and I love it!