We're perfectly fine as we are. It isn't like we have a whole lot of places to pick from to add, either. We've got Guam and a tiny bit of the Virgin Isles, and that's it. And they're both already territories of the US, so they're almost like states.
I don't see how we could add more states than that without forcibly taking over some country or other.
Personally, I think that we need to give California, Texas, New Mexico, Arizona, Utah, and Nevada back to Mexico. The way we took it from them was just wrong.