Mark Blumenthal knows good opinion polling, being an American opinion pollster with 20 years’ experience. This means that his blog is probably the best place for US opinion poll analysis – making him the transatlantic Anthony Wells, I guess.
Most opinion poll interpretation in the press is nonsense, because most journalists either don’t understand statistics or polling methodologies, or don’t think their readers will. Obviously, most bloggers are even worse (I don’t just mean the mindless idiots here – even those of us who understand what we’re talking about tend to let our political views bias the stats we select, hence my focus on Economist/YouGov and Harris polls and pro-Bush bloggers’ focus on Gallup).
Mr Blumenthal (and/or Mr Wells, depending on your geographical focus) are both strongly recommended if you care about why different opinion polls produce such different results, rather than cheering the ones that put your favourite party in the lead.