You are correct about BEL and Banana being really popular right now, but they haven't always been. It's seems they have been pretty stable as high demand lately. Piebald isn't nearly as popular as it once was, probably because it got a little bit over-bred.
Agree Clown, YB acts-like-supers, and GHI are also very popular. OD is in the right combos.
Sunset will be when the price comes down a bit more, but it's still a bit too expensive for most people to invest in.
I think besides those already mentioned, some of my top picks would be Red Stripe, Bamboo and Mojave in non-BEL combos, Mahogany, and Blackhead. With the exception of Mojave, none of these have thousands available on the market, so aren't as likely to sit around not selling. With Mojave, it's all about what's in the combo how well it's going to sell, and it does really well in combos with darkening morphs like GHI or Mahogany.
I predict Wookie is really gaining steam as Kinova cranks out more and more awesome looking combos, and would not be surprised if it becomes one of the more popular morphs in the near future.