As far as animals go, I don't recommend mixing a snake with frogs and/or lizards. There are probably a couple compatible combos, but I recommend either just a snake or just frogs and lizards.
You could do a Madagascar biotope, with plants and animals from Madagascar only. You could keep Mantella frogs, day geckos, small Uroplatus geckos and Brookesia chameleons in such a set up. There are also some beautiful plants from Madagascar that are suitable for the vivarium, like Hypoestes and some Dracaena sp.
You could go with an Asian set up and have several gecko species to choose from and Rhacophorid frogs like gliders (Rhacophorus sp.) or my personal favorite- Vietnamese mossy frogs (Theloderma corticale). You could be more specific and do a Malaysia tank with cat geckos and Theloderma asperum (another type of mossy frog).
But my main recommendation would be South America. Then you could do dart frogs, tree frogs, anoles and/or geckos. With SA flora and fauna, you have a much wider variety to choose from. You could probably get away with keeping an Amazon tree boa or emerald tree boa, but as adults they would make a mess of the tank with waste and activity.
The combination of South American anoles, geckos, dart frogs and tree frogs would give you frogs and lizards that are both nocturnal and diurnal. The there would be activity in your tank at almost any given time. You can use special lighting to see the tank at night. There are many very beautiful species available, many at low prices.
There are also many types of hardy SA plants that are readily available. There are bromeliads like Noreglia sp. (very colorful, wide variety), Tillandsia (air plants) and my favorite- Cryptanthus sp. (earth stars). There are also many types of Philodendron sp. (another favorite of mine) available. They are vine or ivy type plants, and they come in countless colors, shapes and sizes. Pepperomia sp. and Begonia sp. are also very popular vivarium plants. I prefer Rex Begonia types.
When choosing your animals, just be sure to choose species that do not differ too much in size, or you will have cage mates eating each other. Good dart frog choices are some of the larger and more hardy species (tinctorius, azureus, auratus, leucomelas, etc.). Good tree frog choices are Hylid frogs like Dendropsophus marmorata and leucophylatta and Phyllomedusine frogs like Agalychnis sp. (red eyed, black eyed and yellow eyed) and Phyllomedusa sp. (hypochondrialis, vaillanti, and tomopterna).
Most of the SA geckos and Anolis sp. will be suitably sized to live with these frogs. The most important thing to keep in mind when choosing your herps though- ALWAYS buy true U.S. captive bred frogs from reputable breeders! Adding even one wild caught specimen could create a bad time for everyone, especially with the frogs. It may be hard to find CBB anoles and geckos, so I would recommend that if you must buy WC, be sure to quarantine them for a good period before introducing them to the tank, and I would recommend getting them vet checked or at least getting fecal exams for parasites and treating them accordingly.
Michael Novy at rainforestjunkys.com is a dear friend of mine and an excllent source for most or all of the species of frogs I listed above. All are CBB, and almost always bred by him (he occasionally offers surplus CBB frogs from other breeders after he has chosen his holdbacks). I hope this helps. Good luck and most of all, have fun! -p-