The Gallup Poll. June 3-6, 2004. N=599 likely voters nationwide. MoE ± 4.
"If Massachusetts Senator John Kerry were the Democratic Party's candidate and George W. Bush were the Republican Party's candidate, who would you be more likely to vote for: John Kerry, the Democrat, or George W. Bush, the Republican?" If undecided: "As of today, do you lean more toward John Kerry, the Democrat, or Bush, the Republican?" (5/21-23 in parenthesis)
Kerry: 50% (49%)
Bush: 44% (47%)
Remarkably, Nader doesn't really shift the ol' paradigm when he's put in the mix:
Kerry 49% (47%)
Bush: 43% (46%)
Nader: 5% (4%)