Clownfish [Amphiprion sp.] (various species often acclimate poorly to aquarium life and suffer greatly from collection stress, I've seen estimates that as little as five percent of those collected live to be in home aquaria, when possible buy tank raised specimens)
Bangaii/Borneo Cardinals [Pterapogon kauderrni] (rather limited in range and rumors of an unsustainable population if the current rate of collection continues, there are also stories of poor survival after collection, buy tank raised when possible)