Let's say you have a beholder teamed up with some monster who has 20/+2 DR. If the monster is fighting PCs while bathed in the antimagic ray, I know the magic on the PCs' weapons are negated... but is the 20 pt. DR on the monster?
Pkitty, such elementary questions!!!! It is to be ashamed.
DR is a supernatural ability, and hence is negated in an AMF. The only exception I know of is the barb's DR (and that of similar prestige classes). I think this was the first question of mine when the PHB came out.
Piratecat, try hardness. In fact, ALL of an animated objects abilities are extraordinary and not subject to AMF. Just make sure the object isn't animated by a spell (that would be cancelled in AMF), but is created like a golem (which isn't de-animated by AMF).