As a renter, building your own built-in bookshelves is out of the question (unless you butter up your landlord, I guess). But you can get kind of close. Here are a handful of storage solutions that, like liquids and cats, will fill any space. And the best part about modular, design-your-own pieces is that they can be reconfigured to work in your next apartment (and every apartment after that!).
Stacked by Muuto
IKEA Hacked Box Storage
IKEA offers their take on the Stacked series by linking up their storage boxes with simple binder clips. Get the tutorial here.
Clamp Strapped Boxes
Yet another DIY take on the box storage idea, this time from VT Wonen, with a heavy duty clamp strap holding the whole thing together for you.
These more angular boxes from Process can be arranged in some very interesting ways. You can email Process for purchase info.
These little house-shaped cubbies can be put together, tangram-style, to create bigger and better bookcases.
Urban Outfitters Geo Shelf
The Geo Shelf can be stacked together or, one day, wall-mounted for unique and beautiful storage.
Bookstand from Konzept Home
The ceiling's the limit on how high you can go with the Bookstand, a customizable shelf unit from Etsy seller Konzept Home.
You can order the modular BrickBox system in pre-configured solutions, or piece it together one by one on your own.