From the Washington Post:

A new Washington Post-ABC News poll of the Republican field shows Giuliani with a sizeable lead over his three principal rivals. The former mayor was the choice of 37 percent of Republicans and Republican-leaning independents, well ahead of Arizona Sen. John McCain and the still-undeclared Fred Thompson, the former senator from Tennessee, virtually tied at 16 and 15 percent, respectively. Former Massachusetts governor Mitt Romney ran fourth with 8 percent.
Giuliani’s frontrunner status is fueled by a broad-based perception that he is the party’s most electable candidate. Nearly half of Republicans believe Giuliani is their party’s best chance of winning in November 2008; that is three or four times higher than the percentage mentioning other candidates. Democrats and independents also said Giuliani would represent the Republicans’ best shot at holding onto the White House.