In this answer, bacrossland suggests that throwing enemies should inflict non-lethal damage on them. While this is an eminently reasonable suggestion, it leaves one thing open: by RAW, what type is non-lethal damage, and if it is a type in its own right, how is it impacted by damage reduction?
Nonlethal Damage can be any type of damage, or it can be un-typed.
Typed damage (be it from an Unarmed Strike see table or from taking a -4 penalty to use a weapon to deal nonlethal damage instead of its usual lethal damage) would be affected by DR just like lethal damage. It is a not-uncommon house rule that using a normally-lethal weapon to inflict nonlethal damage converts the damage to bludgeoning (using the flat of one's blade, for instance), but RAW don't specify that that happens.
Untyped damage (typically from any of the various environmental hazards) would not be prevented by DR. I've always played with the assumption that falling dealt bludgeoning damage, but the RAW don't support that.