Technically speaking, Manning is the most valuable player. But the other players can all be praised in different ways.
Manning - Most
Valuable Player - Without him the Colts would not be the only undefeated team in the NFL. End of story.
Larry Johnson - He's a fantastic running back and right now he is statistically the best in the league.
LaDainian Tomlinson - Is the most valuable running back in the league hands down. The guy gets every yard that is physically possible for how the defense and blocking is. He jukes, maneuvers, finds holes, better than any other running back probably in history. He is the most well-rounded RB probably in history also. He catches better, he throws passes better, he does special teams better, he is the most consistant and reliable RB in the league. Sorry I had to write all this but ya know he is my boy!!!
Drew Brees - Most Valuable acquired player this year. He is one of the best QB's in the league and at first I was pissed when San Diego let him go but now I see Rivers is just as good if not better so it's all good.

Without Brees, the Saints would not have a winning record.
Donovan McNabb - Best comeback this year that's for sure. The Eagles are struggling a bit but Donovan is back to being Donovan and doing his thing again.