Under our bed, we keep a large metal flat file for drawing storage. This location allows us to store plenty of flat materials without letting the flat file's footprint take up space elsewhere in the apartment.
It puts the bed at a slightly higher-than-normal elevation (about 30"), but it's not uncomfortable or out of the realm of higher typical bed frames..The bed frame itself is anchored into the wall at the head of the bed and rests on the files at the foot of the bed. It's just a standard metal bedframe, which has been modified slightly (the legs have been cut off) to allow it to float.
The added bonus is that there are no bedframe legs touching the ground and marring the floor. We have encountered many wood floors marred by the wear and tear of bed legs over the years.
So, what's under your bed?