I have to find the pictures of this, but the last time we went on a dinosaur binge we cut out a life size T Rex (just the upper part) and put him coming out over the couch. I figured out later that we could have done the whole thing going down the stairs, but there really was something special about having the T Rex looming over you on the couch. I got the idea from Learning Page where you can print out (on many sheets of paper) a life sized T Rex head. This was only 2 D, but lots of fun! I bet it could be done 3D (or at least bas relief) coming out of the wall if you stuffed paper behind it.
Another fun thing (again with the big roll of paper!) was to have the kids draw their favorite dinosaur tail on a double thickness of paper, color it and cut it out. Then you can staple the 2 sides together along the long sides (leave it open where the tail meets the body) and use the paper scraps to stuff the tail to get make it 3D and stiff enough to stick out properly. Finally, we used packing tape to tape the tail to the kid (running it around their middle and folding the last bit of tape so you have an easy way to get it off). The kids (I had a friend's family over) all went nuts!!