For the 5 and 5.5....
-African Dwarf Frogs! Ok, so they're aquatic but they aren't fish
-One or two Mantella frogs?
-A small Salamander or Newt
-Fiddler Crabs (they aren't reptiles but whatever XD)
For the 10-gallon...
-A Paddletail, a couple Firebellies, or some Oregon Newts
-Green, White, or White-Lipped Treefrog
-African Clawed Frog
-Leopard or African Fat-Tailed Gecko
-Green or Brown Anoles
For the 15-gallon...
-Day Gecko (the smaller ones)
-A group of Dart Frogs <3
Hehe...I have an obsession with amphibians and geckos
But seriously, there are way too many reptiles to list. Maybe you can go to a petstore or look online and find a bunch that you like. Then you can research and see if they'd be a good choice
Do you want something you can handle or something more to look at? Oh, and are you interested in snakes too? I left those out...oops.