Storing paintings done on canvas or board vertically rather than horizontally can be a real space saver. It also eliminates the problem of a painting at the bottom of a pile getting squashed and damaged by the weight of the paintings above it. If you've got a little bit of space in a corner of your studio or a garage, you could build yourself a rack similar to the one shown in the photo, which was build by Painting Forum member Jimart.
Add vertical divers to a shelf at intervals so you don't get more than half a dozen or so paintings leaning against one another. Not only does this make it easier to look through them, or pull out a specific painting, but again it helps prevent damage. If paintings are touching, consider protecting them further by covering the front with a sheet of pH-neutral (archival) paper or cardboard. Obviously the painting wants to be completely dry before you do this!