I like all the options you guys (girls?  folks?  y'all?) have used, but I went CHEAP!

The boxes with the Bar Codes on the end are from Dell Computers.  I snagged them from work as the IT folks get the units out of them.

They do hold a lot, and it can be easy to overload the box, which will cause it to come apart.  Here is mold 701 and a ton of casts...


The cavern accessories mold



and I have about a dozen spare boxes in case any of these fail (or I order more molds).


Basic/Gothic: 40, 41, 42, 43, 44, 45, 46, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 200, 250
Fieldstone: 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 701
Cavern: 80, 81, 82, 83, 84, 85, 281, 282
Egyptian: 92, 93, 94, 95, 96, 97, 98, 99, 290, 291, 292, 295
Sci-Fi: 271, 272, 273, 274, 276, 277, 278, 279, 280, 300, 301, 302, 303, 311, 320, 321, 325, 326, 327, 328, 329, 330, 331, 421, 422, 423, 424
Floor and Roof Molds: 87, 201, 202, 203, 205, 206, 210, 211, 212, 220, 221, 230, 235, 240, 245, 260, 265, 267,
Hex Molds: 180

total molds =   104