small pacman frog, 2-3 house geckos or anoles, small leapord gecko, 1-2 small firebellied toads/newts.
depends on whether you are looking for an open air screen vivarium or an all glass aquarium, exo-terra has good terriums about that size and most local pet stores should carry a tank about that size, like a 20 high would be just about that size and a 29 high would be just a little bigger at 30 x 12 x 18. if you want a tank that is wider and longer than it is higher than you would be looking at a 30, 40, or 50 gal breeder tank.
hope this helps
2.0.0 whites treefrogs
0.1.0 mexican leaf frog (P. dacnicolor)
1.0.0 golden treefrog
0.0.1 green treefrog
1.0.0 southern leapord frog
2.0.0 green frogs
0.0.1 bullfrog
1.0.1 smokey jungle frogs
2.0.0 pixie frogs
1.0.0 pac-man frog
3.0.2 fire-belly toads
0.0.1 yellow-belly toad
1.0.1 fire-belly newts
1.0.0 blue-spotted salamander
0.1.0 yellow spotted salamander
1.0.0 barred tiger salamander
1.1.0 blotched tiger salamander
1.0.0 eastern tiger salamander
1.0.0 gray tiger salamander
0.0.4 koi
0.0.1 fantail comet
0.1.0 green iguana
1.0.0 german shepard
1.0.0 quaker parrolette