For folks looking for impressive safety cages for production based cars I suggest looking at the Australian V8 SuperCar roll cages. There is a lot of good ideas, one being cross bracing the floorpan. We all assume the floorpan is stiff and only really pay attention to the side and top sections.

I keep a file on roll cages that I see pics of on the net. Many of them have influenced the design on my Volvo 240 (cage goes in this winter, finally).