First of all, make sure that the stackable media storage unit will hold the type of media that you need to store. (It’s easy to get different types of media and their associated shapes confused!) Then, look for drawers that pull out, so you can easily view all of your CDs or tapes with just one smooth motion.
We’d also look for a unit that has several different drawers so you can organize your media, and for closed-front drawers that are aesthetically pleasing so you can avoid the often very-busy feel of a typical media storage cabinet.