This advice might be a decade or two out of date, but you all are clever souls, so this suggestion may still be of use to someone out there.
The simultaneously goofiest and most practical storage solution we have in our house is this unassuming wooden unit. It's 29 inches tall, 24 inches wide, and 12 inches deep. It's lived on an open spot of our walls for over a decade. And inside? Paperback books.
We discovered someone getting rid of this unit many moons ago. Astute individuals may realize what it began life as: a VHS cassette holder. Of course, nearly all our VHS cassettes are gone nowadays, and they were gone when we got the unit. But it was a decent size, and – hey, free! – so we brought it home. That's when I discovered it's the perfect size for mass-market paperbacks.
This size of books has been the bane of my storage existence for 20+ years, because they take up a lot of wall space if you put them on a shelf spine-out. But if you stick them in boxes, you can't see what you own, access them easily, or indulge in a manic gamebook revelry on a quiet weekend. This unit was a "best of both worlds" solution, taking up no more space than a traditional bookshelf, while allowing for easy access to double the storage.
As noted, this advice is probably a decade-plus too old to be widely useful, but if you happen to stumble across a unit like this in a second-hand store or on the side of the road, you might now realize its value. If you go shopping for one, you might want to bring a paperback or two to see if they'll fit the specific unit's configuration. Plus, if you're still holding onto some VHS tapes, you can make them at home on the same shelves!
-- Steven Marsh