For those not boxed or in old rental cases, I, too, have them sideways on a shelf, but with these on: https://www.amazon.com/dp/B00AAIDNTW/ to keep the dust out - they stack neatly when you alternate the orientation. Hit the edges with some fine grit sandpaper to make sure they're not sharp enough to potentially scratch the plastic or labels. Rental cases are more ideal if you have the shelf space, but are getting harder to find. Otherwise, there are purpose-built cart drawers that were a thing in the late 90s. Might be a good option depending on the size of your collection. Rubbermaid-type drawers may also work well.