What about removable media, e.g. zip disks, tape cartridges, maybe even disposable media? It's a recurring purchase as long as the consumer needs more storage, it's massed produced (multiple units of the medium per one unit of the drive that uses that medium)... In terms of margin, you wouldn't expect them to be much but in proportion to total production cost, they might bring in a sizable chunk of the pie.
edit: this is guesswork