It seems to be the sternum (underboob area) that's a pretty popular equivalent at the moment. And as much stigma as the phrase holds I think tattoos in both those placements look great. And fair play to the girls that have got them (at a substantial size still) it's not a nice area to get tattooed. Especially the sternum! They're not for the faint hearted. I'm dreading the lower back and beyond when I get my backpiece done.