I heard on Fox News awhile ago that it would be Mitch McConnell.
I've also heard that Trent Lott is trying to get his old job back.
Right now I put the odds at:
McConnell 70% Lott 20% Other 10%
Those odds are for Majority Leader only and based on my opinions/observations. They do not apply if we lose the majority (won't happen), then anything could happen.
Addendum: McCain currently runs the Senate, making the Majority Leader job pretty thankless.
McConnell has it in the bag, unless he praises Hitler in a speech or something. Not only does he have the ability to control the caucus, but he has access to money. Everyone knows he's coming in. Lott can't do anything to defeat him for the position.