Inventory storage is an ongoing challenge for me, but after trying what feels like a million different methods, I've finally found one that I actually like: IVAR shelves from Ikea. They're affordable, easy to put together, some in a few different sizes, aren't total eye-sores, and customizable to fit my needs.
Ikea offers two different options for shelf-depth and they have different shelf-lengths as well. The units also connect so you can have many in a row with very little gap between them. You can decide what height you want each shelf at and you can fit as many shelves as you need in one column. You can also add corner shelves and doors to the front as well. Overall, I really love these shelves!
They also work great for storing greeting cards when paired with these boxes from Amazon (affiliate link), which is how I keep all my cards organized in my office (pictured below)!
Here's a few other storage bins & organizers that I love to use for my business! (affiliate links as well!)