I do approve of pirate radio though, people getting together playing music for themselves and their friends has to be good right? So... londonpirates.co.uk is a site worth a look, I love the gallery section with all the 'make do' technology.
Graffiti is a similar topic, you might not always approve of the location, but you often have to admire the talent... graffitiresearchlab.com (although not London-focused) has some amazing ideas. I especially like the light based forms of tagging (flickr slideshow)... maybe we could see something like this in the capital.
If you really are anti the whole graffiti thing but still would like to express your inner urban artist, take a quick look at graffiticreator.net a great way to paint it up without disturbing the peace.
Also worth a look... tubephotos.com... there's an eerie feeling to these pictures, very interesting. If you do manage to take an amazing photo of London you could try The Rasterbator... this site will create an enormous poster of your work to impress your friends.
That's all for now, see you next time. Enjoy London.
By Doc Rogers – www.docrogers.co.uk