Acrylic boxes in the shape of Legos for holding Legos. Insanity! They stack quite well, though for the next version I'm going to make the "nubs" a smidge smaller, they're a bit finicky as it is.
Each box holds at least 64 of that sized Lego, and the larger ones hold a few more. The 1x1 box is 40mm per side.
The boxes were generated with OpenSCAD, the code for which is available on my blog if you want to make other sizes.
Cut pieces from 3mm thick acrylic.
Place the bottom (with the holes) on top of the lid (without the holes). Put a dab of acrylic cement on a "nub" circle and attach it to the lid, using the bottom as a guide.
Once each nub is tacked down, remove the bottom guide and run a paint brush with acrylic cement around each nub to fix it in place. Allow to dry.
Assemble the rest of the box, leaving the lid free.
From 1mm acrylic (or whatever the thinnest you can find is), cut a rectangle to fit the inside of each box (to keep things from falling through). The dimensions of the rectangle can be calculated by n*40-6, where n is the number of nubs on that side. Please note if you used 1/8" acrylic rather than 3mm (check it with calipers if you arne't sure), you'll need to adjust a bit or the bottom liner won't fit.
If you don't have any thin acrylic, you could use Mylar or any other transparent plastic sheet.