Hector Balderas comes to mind.
Newly elected small state Attorney General?
It's not like they'll just have one candidate. There's likely to be a shortlist of some kind. People I see on it.
Mark Warner: Virginia. Very experienced. Better natural politician than Kaine. Successful businessman.
Tim Kaine: Virginia. Still pretty experienced. Demonstrated discipline as Warner's Lieutenant Governor/ DNC Chair. Governor who developed reputation on foreign policy issues.
Cory Booker: Popular African-American Senator with executive experience, and a comfort level in front of cameras.
Julian Castro: They've kinda built a potential Veep with him. Young Hispanic guy with a resume that looks okay.
Xavier Becerra: Latino with experience in congressional leadership, and a comfort in front of cameras as a prominent party surrogate.
Brian Schatz: Young progressive Senator in interracial marriage.
Chris Murphy: Young progressive favorite getting attention as policy leader. The Clintons were concerned he might run for President.
Michael Bennet: On paper, he seems to be the best. Age-appropriate Senator from the crucial swing state of Colorado, with a background in education, always one of the most important issues. Has not developed much of a national profile, though.
Tom Vilsack would be good too.
Vilsack has some advantages (good surrogate in the Midwest, resume) but he's probably too old.
What about Marilyn Mosby? She seems like the traditional attack dog role that the Clinton campaign needs.
Now I think you were making fun of me with the earlier response.