There are others out there, this is what I came up with.
This lets you hang your filament spools from a 1 3/16" (30 mm) closet rod.
The lip on the end is 54mm, works great with my 1 kg rolls of Monoprice filament that I've been using.
But mikepf, you say, what if they start to sag?
Then you get another 30 mm closet rod and run it through the middle of the spools, then you print out two of the newly uploaded closet rod hanger and use the hangers to hold it up and prevent the sagging. You'll need to remove the rod to change out spools, but this works out nicely if you just feed from the hanging spools to your printer.
Update (Cinco de Mayo edition)
On request, a new model has been uploaded. The
-smaller spool one has a 48 mm diameter lip and a 44 mm spool holder.
I've printed some of these with no additional bed adhesion, some with full brims, some with rafts... since it does have a rather large base, it can warp/lift while printing, and I've had one break free of the bed at about 80% completion (the second orange one in the picture of them in use).
These take about 8 hours to print on my A8.