I'm a fan of simple vertical tanks myself. I usually find a nice, tall piece of cork bark and either wedge it in or attach it to the tank and mount broms and vining plants. I use leaf-litter and a variety of begonias. Here is an example of one of my simplistic 20gallon verts which houses a trio of Ranitomeya Amazonica poison dart frogs. I'm not sure how to adapt this concept for tree frogs though.