The British Humanist Association are running bus ads in London with the slogan:
"There's probably no God, now stop worrying and enjoy your life"
Tiny campaign. Big impact.
In fact, this Nielsen BlogPulse run for the term 'probably no God' shows that even suggesting they would spend the money generated as much hype online as actually spending it.
And a Thought for the Day from The Guardian (TftD is incidentally going to broadcast its first non-religious message as a result of the campaign.)
"The ASA has received 141 complaints about the Atheist Bus Campaign which launched earlier this week on buses throughout England, Scotland and Wales, as well as the London underground. However, 39 of the complaints are regarding newspaper and online articles about the campaign, which the ASA has no power to deal with."