It's definitely solanaceous.
I would guess from there it's either a Brugmansia, Datura, or an Eggplant.
The leaf shape, arrangement, and the way the new leaves are forming, as well as the growth habit, are consistent with any of these three families. You can probably help distinguish between the three by crumpling a leaf and smelling it. Datura and Brugmansia have strong distinctive bitter smells I don't really know how to describe it. I don't believe that eggplant has much of an odor but I will have to check when I get home today.
The more I look at your photo the more I believe is is a brugmansia from the way new leaves are emerging from the node between the leaf and stem, but you will find out eventually as it grows more and flowers.