I still store all my flat metal dies in CD cases with a magnet sheet adhered inside. You must buy the older thicker CD cases and simply remove the black insert. I have found them at Staples in a box of 25 for $9.99 then I purchase the magnetic sheets in a roll from hobby lobby for $9.99 you can also buy them in sheets but if you have a collection it is less expensive to buy the roll. Simply pop out the plastic insert cut the magnet sheet ( self adhesive ) to fit in both sides of case and add your dies. Obviously this does not work for the newer oversized dies and those are just left in the original package and stored on a clip it up. My sizzix and Tim Holtz etc. are stored in a white 4 drawer cube from Mikes. They fit perfectly. Once again the 12inch long ones dont fit but they do fit in the 2 drawer cubes.
Hope that helps.