The local big box store has a receptacle for toner cartridges. Hit Best Buy, chuck them in there, call it done, the end.
I had a lot of toner cartridges as well, but no use in keeping them. They are not going to appreciate in value, and as time goes on, that toner cartridge format will be used by fewer printers, so might as well dispose of them properly (and properly isn't the trash can.)
I'd likely waste more $$ on gas packing up and driving to a Best Buy to drop off a single cartridge, than would be saved by recycling.
And as other posters say..what guarantee is it that BB is recycling them in some fashion?
Some things are trash, and crap like this isn't worth my time to drive all over town trying to find a specialized bin to toss it in. I'm not going to keep 3-4 different trash cans taking up limited room in my kitchen to sort shit out, why would I drive all over town to throw out one toner cartridge.
My taxes/fees pay for garbagemen to pick crap up and haul it off. Why not use them for what they are there for?