Colorful, tropical, eccentric, unique, showy, flashy, soothing, gorgeous, amazing, stunning, hypnotizing
Betta Bonanza (I know, tacky but sticks in your head!)
or even better...
or if you are already skilled in betta breeding....
Better Betta Bazaar
Better Betta Beauties
hmmm... or if you want to go with something not so cheesy...
Bubbles and fins
(but then these names leave one wondering which fish you are selling)