TradeSports.com has futures on events.  Based on bids and offers for contracts, they have the Cards as the front runner for the NL pennant.  What I don't get is that they have the Cubs ahead of the 2005 NL Pennant winner, your Houston Astros!  
Anyway, this site is very interesting to watch as it does generally predict things..
So, here's the current info on the NL Pennant: 
Code:
 
STL  Bid 24.4  Offer 26.5  Last 24.9
NYM  Bid 18.5  Offer 20.5  Last 19.0
ATL  Bid 10.5  Offer 13.2  Last 12.0
CHC  Bid 8.2   Offer 9.5   Last 8.9
LAD  Bid 7.5   Offer 9.5   Last 7.5
SFG  Bid 6.7   Offer 7.8   Last 7.4
HOU  Bid 5.6   Offer 6.8   Last 6.0
 
 No one else above 5.
This is on a 100 point scale.  Generally 0 means 0 percent chance of the event happening and 100 means 100 percent chance of winning.   Last trade is usually the thing converted to percentage.