What do you do with your old toner cartridges?

I currently work at a Vocational Education
center as one of the two people in the IT
department. Recently when cleaning the office
area we discovered that we had accumulated
quite a few empty ink and toner cartridges from
a verity of printers. In the past we did business with a local company that refilled old
cartridges that gave us a slight discount off
the price of refilled toner when we returned
cartridges, however this company has gone out
of business recently, so we are looking for a
new solution for the cartridges, What do you do
with your empty cartridges?