I have two books on it that I got recently. I too have been learning it.
Moden Benoni by Andrew Kinsman
and
Starting out: Modern benoni by Endre Vegh
I think the two books are pretty good so far and I have been learning alot. I plan on only playing the modern benoni though, not the other benonis.

I'm planning on picking up the benoni defense, but I've noticed that they are quite a few books on it. Does anyone have one they would recommend? Thanks!