Adult crested geckos need at least a 20gallon high tank, however a 10 gallon is good for a juvi or baby. A single leopard gecko can live in a 10 gallon for its entire life. Have you thought about the American Chameleon the Green Anole?They are easy to care for but do require UVB lighting, but a 10 gallon is enough for one. Finally there are many frogs like red eye tree frogs, green tree frogs, or whites tree frogs that could live in a 10 gallon for life.
1.0 Veiled Chameleon 0.1 Leopard Gecko 1.0 Crested Gecko 1.0 Waxy Monkey Tree Frog