You might find it worthwhile to look at this thread... 8 pages of suggestions of different colubrids:
http://ball-pythons.net/forums/showthread.php?t=67180

Right now we have 1 BP and 1 corn. We love them both and I 2nd Bruce (loft lizard) in saying that they make a good complement to each other. The corn is much more active and less shy. I've even seen her poke her head out of her hide to see what is going on when I walk past her enclosure and make a shadow. And of course you get the difference between a heavy bodied snake and a more slender one. Plus corns come in a whole rainbow of colors, and since they've been breeding corn morphs for over 50 years (as opposed to I think it was '92 when the first albino BPs were bred), most of those morphs can be had very inexpensively.