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.

Echinocereus reichenbachii albispinus

This small cactus with all white spines is almost as pretty with buds as it is with flowers.

Lobivia pugionacantha 'culpinensis'

Pugio is a name of dagger, a favorite side-weapon of roman solders. In cactus names it usually refers to long stubby spines, like in this species.