According to Baseball Spreads the Tampa Bay Rays are the favorites in the 2008 World Series. Depending on the source they are -150 to -155 odds on favorites. This means a player would have to bet $150 or $155 to win $100 if the Rays can win the World Series.
From Squidoo -
Recent World Series History:
The most potent offense in the post-season, this team relies heavily on the homerun, with strong power hitters Howard, Burrel, Werth, Utley and Rollins. Their pitching is under-rated by most.
Tampa Bay Rays
The upstart franchise features one of baseball's lowest payrolls and is full of home grown talent. With the current contract set-up this team should be near the top of the AL East for the next three seasons before having to drop payroll. They hold the best regular season record of any team left in the 2008 MLB playoffs.