To be honest, I think you could really put anything in there if you wanted. It's all about how you go about it, of course. I had no issues keeping my ball python or my corn in a glass tank (mind you, the largest was a 30gal). You just have to mess around with equipment a bit.. as you would with any new set up though. Personally I found more troubles with PVC than my glass tanks, but that's besides the point.
If you want something to keep with ease - if you are looking for another snake - anything with low humidity or "room temperature"ish requirements would probably work the best with the lowest additional cost to you. You could also add a divider if you wanted two of something, or perhaps an adult of whatever species you are interested in.
Best of luck!