The first 5 that popped in my head that I didn't see named off yet:
Bumblebee Oscar:
L305 (lemon fin):
Lipstick tang:
Rusty Angel:
Jack Dempsey:
Ippo, my Jack; yes I know they are super common... Sorry for the fuzzy phone pic (only good one I had in my phone); I didn't care for these guys before but he's growing on me.
i'm surprised a black aro hasn't been mentioned yet or any aro for that matter I personally think a goonch catfish is quite the sight as far as sw any of the billfish or tuna species are mine and I 100% agree with what rob said about cephlapods case in point the giant squid
There is so many fish we love and see beautiful, but tourist are probably going to like smth colorful. SW fish are much more colorful in general. Aside the mandarin goby I also like the colors of firefish like Nemateleotris
or orange stripped prawn goby http://www.liveaquaria.com/product/prod_display.cfm?c=15+31+197&pcatid=197
also bannerfish look nice like the Moorish idol for example
That being said there is also FW fish with great colors, someone already mentioned Xmass fulu and there is also pundamilia nyererei
discus fish are a royalty of FW aquariums and they come in many colors
and as someone mentioned halfmoon bettas that also come in many colors