I agree with Kavinsky with most of the maps he listed except for the following:

zm_hospitalv4 - I've caded other rooms myself. As long as there are people that don't ruin it that is. Other than that, I would usually hold up pretty well there.
ze_backmesa_escape_final - Not so keen on the escaping part, but golly I get a lot of kills vent camping there and trying to make an epic escape at the end which usually leads to an epic fail.
zm_highschool - I've seen other rooms with decent barricade objects.

To add to the list:

All regular CSS deathmatch maps.
zm_island_defence_v2 - not a whole lot of barricade spots...just map exploitation (i.e. wall glitching and pit hiding)
zm_umbrella_corp - the objects you cade with just fail...a fast zombie can get through any barricade spots in the map
any maps that contain the word "office" in it EXCEPT for zm_vc2_lila_off!ce (I think that's what it's called. You can camp the power line there or the letters in the back of the map.
all versions of elevator escape because the nuke takes so damn long to detonate after calling for it.

That's all I can think of on the top of my head.