High Charithea,
Nice flower. Do you know the names of any other of your cacti? Looking at the second picture you posted, the one immediately behind your Gymnocalycium (on the back row, right) looks very much like a recent posting of mine on the plant id. pages. I hazarded a guess at Echinopsis arebaloi.
The cactus to the right of your Gymnocalycium, the one with the reddish spines, looks like a cactus I have which I want to post on the id. pages at some point. Any help you can give would be very much appreciated.