Looking for some info, getting new snake.

[BoaBoi]

Ok guys, I currently have a 4' Columbian redtail boa. I've had a royal python that I got sickly and didn't live. So I'm use to nothing but large body snakes. I've hadnled snakes out of the yard and kept a few green snakes for a week or two then let them go. ~ But now I'm wanting to get a Colubrid, but what kind? And how do I go about it as far as the feedings. Pythons start out pounding adult mice and baby rats, but I'm pretty sure these guys cant. I'm going to a reptile expo this weekend to get one, and I need to know what snake to get. I have a cage ready and I know how to house snakes properly now I just need to find out the final details before I get it. `~` Any input is very appreciated.

P.S. I want one that will get pretty long within a few years, and I have heard that a black rat snake fits that.