I don't know exactly how to tell the different types of ficus apart. If you go to Lowes or Home Depot and buy a ficus, and it looks like your everyday ficus, I can almost guarentee you that it is benjamina. I doubt you could find much else different without going to a greenhouse. However, I've never been a big fan of ficus. The ones you buy in the store are raised outside, so when you bring them inside, they drop most of their leaves, even if you stick them under six 48" fluorescent day glow bulbs. For me they just get to be a big ugly bundle of sticks with a few leaves. They can also give your Chameleon an eye infection (although I have never had this happen, I've read that it's quite possible.)
I prefer umbrella plants, pothos, and sweedish ivy. They all thrive under grow lights, and tolerate the chameleons munching on them every once and a while. Here's the plant list I used last time I went out looking for plants, hopefully it will help:
http://home.att.net/~chameleons/safeplants.html
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1.1.0 Sunburst Veileds (Oscar and Lizzie)
1.1.0 Azureus darts
2.3.0 Mantids
1.0.0 Albino Pacman (Grumpy)
2.0.0 White's Tree Frogs
0.2.0 Cats (Oreo and Doodle)