Eriosyce chilensis albiflora

Flowers on that plant are not exactly white unlike the name suggests.

Opuntia microdasis

Unexpected buds on the small-padded white variant of Opuntia microdasis that I've picket at local garden store a while ago.

Sulcorebutia albissima

Sulcorebutia glomeriseta

This species looks a lot like Rebutia senilis, but of cause belongs to a different genus and not closely related.

Ferocactus glaucus

This spineless form is common in cultivation. I'm a bit fascinated with geometrical oddity of spineless cacti.

Loboiva haematantha ' jasimanensis '

Coryphantha maiz-tablasensis

This is one of the more popular Coryphanthas among the collectors, probably due to it's relatively resent discovery. It is an interesting plant, but flowers are small - despite the impression you may be getting from my picture.