The Guardian and the British Humanist Association have begun an "atheist bus campaign" to counter religious advertising in the UK with some atheist counterpropaganda. But while their message - "There's probably no God. Now stop worrying and enjoy your life" - is one I agree with, and it will undoubtedly generate a few smiles while offending some people who deserve to be offended, proselytising is something religious people do. More importantly, I just don't see the point. I don't waste my time believing in gods - but I don't waste my time not believing in them either. The whole idea is simply completely irrelevant to my life. Why bother to stick that on the side of a bus? IMHO, its caring far too much about something no-one should be caring about at all.
Still, if you do care, you can donate online here. They've already reached their initial target (it only took them a few hours after going live), so they're extending the campaign.
(And on a related topic: Salon has a review of Phil Zuckerman's book Society Without God: What the Least Religious Nations Can Tell Us About Contentment, which is quite interesting. I doubt the Danes and Swedes would bother with an atheist advertising campaign either - but then again, they have no need to).