Does it have to be a 55gallon?
If so your best options are:
- Carpet Pythons
- Brazilian Rainbow Boa
- Red Tail Boa (BCI or BCC)
- Macklott's Python (really cool partial water snakes)
A smaller cage would provide for some of the best display snakes of all. The Green Tree Pythons or Amazon Tree Boas. Emerald Trees are also good but less forgiving as far as husbandry is concerned.