I actually posed a similar question a couple of weeks ago (2/26/09) - see if this link works. http://www.mamasource.com/request/2895395843668443137
I actually found that the huggies overnites didn't work for my now 7.5 month old son, even in a size larger (they sell them at Toys R Us, Shoprite, etc.
But the Pampers Cruisers ULTRA ABSORBENCY are the BEST!!!! The first time I tried them, he had a small amount of leakage. Then when I used them again and really focused on bringing the front part of the diaper higher up than the back, it really did the trick! There is a green absorbent layer that lines the diaper. Buy them in one size larger as well.
Unfortunately, you can only buy them in BJs or online at one or two websites. But they are worth the investment. Both The Cruisers Ultra and overnites ar going to be more expensive than the typical diaper, since they are ultra absorbent.
Good luck!