Beginning to think about grad school. Conservation, Ecology, Environment?

So I def got a late start, you would think I would know what I want to do by now. So I am 33, finishing my undergrad in Biological Science at Arizona State. Plan on graduating in 2012. I think the hardest decision for me is going to be to try to narrow my interests down a bit. I am looking for ideas on how to decide on what exactly I would like to study. Thank you in advance. :)