I use clamshell binders by Unikeep that stand square and are designed to be upright and they have a very small ring profile with square rings, so they fit tighter on a shelf if your space is limited, which is my situation. They are 1.5" thick, 100% polyethelyne [no metal to rust or bend, and no acidic cardboard] and the profile is just barely more than that.
http://www.unikeep.com/binders-and-a...-ring-binders/