From the upper left corner, row-wise: Mammillaria elongata. Chamaecereus, probably a hybrid. Another Mammillaria. Yet another Mammillaria, perhaps M. bocasana? A Mammillaria! Reminds me of M. karwinskiana, but I am not sure at all. Probably something from the Echinopsis/Lobivia/Trichocereus group. Flowers might give a clue. Mammillaria elongata again, but a form with brown spines. Sorry for not being more specific, but Mammillaria is a big genus, and I have only grown a handful of them.
