There are five more senators who have either given signals that they'd support the public option or, when push came to shove, would be more likely than not to do so:
44. Tim Johnson (SD). Appeared to commit to the plan over the weekend. Should be regarded as a highly likely 'yes' vote.
45.
Robert Byrd (WV). Has yet to take a position publicly, probably because he's been ill. But Byrd is generally pretty liberal on economic issues, and his colleague (Jay Rockefeller) is a vociferous supporter of the public plan. The potential barrier here, as in Kennedy's case, is likely Byrd's health rather than any philosophical concerns he has about the plan.
46. Amy Klobuchar (MN). Howard Dean's website lists her as a supporter. She's been decidedly more ambiguous in e-mails to constitutents, and Minnesota has lots of skin in the health care game in various forms. Still -- although Klobuchar is not as liberal as you might expect from a Minnesota Democrat -- this seems to me like an eminently whippable yea vote.
47. Ron Wyden (OR). Wyden's indifference to the public option is a little odd -- he's ordinarily quite liberal -- and may reflect his desire to promote his own health care alternative. Once it came time to vote on the actual, non-Wyden bill, I'd expect him to vote yes on the public option.
48. Herb Kohl (WI). Ostensibly supports the public option but with a lot of caveats: that it be "bipartisan", etc. Realistically, any public option that the Senate is considering is likely to be fairly watered down, moving Kohl into the probable yea vote category. But the co-ops concept might also be alluring to him.
Now, here are the senators that Bowers lists as maybes but who I think would be relatively unlikely to vote for the public plan. Not included here are Joe Lieberman and Susan Collins, who he lists as definite no's.
http://www.fivethirtyeight.com/2009/08/how-many-votes-does-public-option-have.html