I use different size carboys. I have 6 gallon, 5 gallon, 1 gallon and half gallon for all my secondary storage. It gets kind of strange looking at my wines. All the different size jugs sitting around. But it gets the jog done.
I have also thought about the marble, or like things. I saw bags of them at the dollar store. Can't beat getting them for cheap.
On Deck - Crabapple Wine, Delirium Tremens
Primary - Surly Furious clone, Kolsch
Secondary - Hofbrauhaus Lager
Bulk Aging - Brewtopia Barleywine, Pomegranate Wine, Red Table Wine, Wild Fox Grape Wine, Blueberry Wine