The final two are Biden and Bayh

Both Joe Biden and Evan Bayh have been given prime time speaking slots on Wednesday night, the same evening when Obama's VP pick is scheduled to speak.  True, candidates could be moved around after Obama makes his pick, but most would agree that this is an indicator that Obama has narrowed his vice presidential list even more.

And according to one source, the Obama camp is leaning towards Biden:

I'm just passing on the latest I'm hearing--that Sen. Joe Biden (D-Del.) is moving up on the list of potential running mates for presumptive Democratic nominee Sen. Barack Obama (D-Ill.). While Obama's heart may go towards Virginia Gov. Tim Kaine--his head takes him to a more experienced pick, a Sen. Evan Bayh (D-Ind.) or Biden, chairman of the Senate Foreign Relations Committee.

Bayh, Biden, Kaine and Sebelius, in my view, look like the top-four from what I have been reading over the last week.