The numerical contradictions happen to be my favorite ones. Ahaziah's age when he ascended the throne for instance (42 in one book, 22 in another; note: some modern translations make the correction on their own). The number of horses/sheep solomon owned is another good one. Gen 1: (trees before man) vs. Gen 2: man before trees. I believe there is also one about the age at which Terah [abraham's father] died (if anyone knows this, please post it, I can't seem to find it).
However, I would encourage you to be prepared for the worst. In the fundamentalist mind, information about the bible is understood in a different way. Since the fundamentalist believes, a priori, that the bible is without contradiction, there *must* be an explanation. Just to avoid a good deal of frustration, have the person you're debating do 2 things; 1) define contradiction and 2) provide an example of a contradictory passage in a book or magazine. This way, you can pin him/her down on their definition once they come up with exceedingly unlikely excuses for biblical mistakes.
Good luck!
-Shea