Mammillaria nejapensis. I bought this cactus just this year. I like the contrast of the bright green body with the hairy areoles and light-colored spines. The flowers are also a little different with the stripes of red against the white. These flowers last a couple of days before closing.
Notocactus haselbergii. I thought these blooms never would pop open! They have a waxy finish on the petals, so they will stay open a few days. The waxy blooms seem to last longer than the more fragile, softer petals.