From HardballTimes.com:  

Win Shares. Invented by Bill James. Win Shares is a very complicated statistic that takes all the contributions a player makes toward his team’s wins and distills them into a single number that represents the number of wins contributed to the team, times three. The website has tweaked James’ original formula somewhat.

Win Shares Above Bench, or Baseline. WSAB is a refined approach to Win Shares, in which each player's total Win Shares are compared to the Win Shares an average bench player would have received, given that player's time at bat, on the mound or in the field.

This is an important adjustment to Win Shares, as we discovered during the 2003-2004 offseason. The bench player approach is explained in this article. It is essentially 75% of Expected Win Shares for all players except Starting Pitchers, for whom it is 60% of Expected Win Shares.

With all that said here there five most valuable players:

• Lance Berkman - WSAB = 18
• Albert Pujols -  WSAB = 16
• Ian Kinsler - WSAB = 16
• Justin Morneau - WSAB = 16
• Josh Hamilton - WSAB = 16