Green Tree Frogs(Hyla cinerea) are a great little tree frog to start out with. Unfortunately, like what was mentioned before, they are nocturnal so you won't see much activity during the day unless you feed them at this time, especially with crickets.

Crunchy Frog is right about the vivarium size. It's okay with young frogs but as they mature they will need more room. 20 gallon tall is the way to go. Also, if you plan on using any live plants in the enclosure choose ones that are strong and have broad leaves. Mature Green Tree frogs can really tromp all over live plants.

You are in luck because I believe all Petcos are going to be having their $1.00 a gallon sale starting on December 28.

Good Luck!