Politico has their requisite list of potential candidates:
Kansas Gov. Kathleen Sebelius; Michigan Gov. Jennifer Granholm; Mary Beth Maxwell, executive director of American Rights at Work; Ed McElroy, former president of the American Federation of Teachers; former Rep. David Bonior, D-Mich; Maria Echaveste, former Clinton White House adviser.Sebelius and Granholm appear on almost every one's list as a potential nominee for something and the number of "somethings" is narrowing, so if conventional wisdom is correct that means they should be given pretty serious consideration. I have seen some stories that Sebelius and the unions in Kansas did not always see eye to eye, which might be an issue for her.
Bonior's name has been on most lists and although he has publicly disclaimed his desire for the position continues to be. Bonior himself supports his compatriot at the American Rights at Work organization, Mary Beth Maxwell.
Maxwell might be acceptable to both the AFL-CIO and the Change to Win unions which could be a big plus for her chances. She also would be the first openly gay Cabinet member. For more on Maxwell check out Mary Beth Maxwell for Labor Sec? from the American Prospect and Union Activist Mary Beth Maxwell on List for Labor Secretary from the Wall Street Journal's Washington Wire.
I have not seen McElroy's name mentioned and I don't know any background, but given some of Obama's views on education, doesn't seem to be the most likely fit. I don't know if Maria Echaveste has any particular labor expertise or backing or is just a well known Hispanic. Given that there has been considerable talk about the lack of Hispanic representation in post-election appointments that could be a factor.
Two names that aren't on Politico's list -- Dick Gebhardt, the former Majority Leader in the House and Representative Linda Sanchez (D-CA) who was endorsed by the Hispanic Caucus for the position. (She was also endorsed by the leading gay rights organization, the Human Rights Campaign, an endorsement she now shares with Maxwell.)
Even though Politico is a great site and is often insightful, I wouldn't bet on the accuracy of any of these projections. Until we start hearing "definitive leaks" (an oxymoron if there ever were one), we will just have to wait and see who is going to be the first new Labor Secretary in 8 years.
But certainly in the world I work in, it's a very important question.