An August 16-18 poll by the London Economist, using a relatively large sample of 1799 respondents, showed John Kerry with a firm lead of 48% to 41% over George W. Bush.
What DonkeyRising Doesn't mention is that this poll shows Bush's approval rating at 39%! To my knowledge this is the first time he has broke into the thirties. He's getting in Poppy territory.
As Atrios observed, the medias failure to report the story of Bush's low approval rating is one of the biggest unreported stories in this election cycle.