Pituophis catenifer sayi AKA Bullsnake. I've have several of them myself, they make a great pet. They can get fairly large and have great personalities. They're more active then a ball python and have a faster metabolism so they'll need to be fed (and cleaned up after) more often. They can be fairly messy, I've had some before that seemed to like smearing their crap all over the cage so it's best to keep the substrate and cage furnishings fairly simple.