The latest Zogby American poll came out today:

[L]ikely Democratic primary voters give a plurality of their support to former Vermont Governor Dr. Howard Dean (16%), whose campaign has been gathering support in recent polling. He is followed by Massachusetts Senator John Kerry (13%), Connecticut Senator Joseph Lieberman (12%), and Missouri Congressman Richard Gephardt (8%). No other candidate polled more than 3%.
The same nationwide survey also asked Americans how they would vote if they had to choose today:

Just two in five (40%) said they would choose Bush if the election were held today, while 47% said they would elect a Democratic candidate. In August polling, respondents were split (43% each) over President Bush or any Democratic challenger.

Here is a link to the Zogby site with details on the poll:
Click here