Toner Cartridges - HP
HP's scheme requires you to register before recycling anything, giving you the ability to then request postage-paid labels for both toner and ink cartridges. This scheme has the added advantage you can recycle just one cartridge at a time instead of having to stockpile them if you're a home user, or arrange bulk returns for bigger businesses.
Accepts: Ink cartridges, toner cartridges