UPDATED: added a super-strong version of of the bracket (SBH, Spool Bracket, Heavy). Whereas a stiff downward jerk would break the original version, the improved version will withstand much more force and weight. Use the original "2spool_bracket" at your own risk (it is also the one of the two that will fit in a Rep 2/2X spool slot).

UPDATED AGAIN: Provided a "SnubWSB" (wire spool bracket), which is better suited for cramped (cough NEW YORK cough) places, but will only carry 1 5th gen spool.

Wire racks, the kind sold by U-Line and other manufacturers of industrial equipment, are a fantastic solution for any number of storage situations, including Replicators and the filament they use.
This bracket is designed to hold filament spools outside of regular shelf space on these wire racks. They can hold up to 4 full 5th-generation spools at once, printed at 10% infill with only 2 shells (default Makerware low settings).
This bracket was designed explicitly with the long sides of the wire shelves in mind; it will not fit on the end caps.

Default low settings will make brackets that hold at least 8 lbs (spread across the arm).
I imagine higher shells and infill will provide even tougher structures.