My family runs through a lot of ink, and I've tried several different methods of stemming the cash hemorrhage as a result of paying upwards of 30-dollars per new cartridge. Walgreens, a drug store chain near us, offers cartridge refills for about half what we normally pay and has one-hour turnaround.
I'm sure everyone's had the horrific experience of spending 15-20 dollars on a "refurbished" cartridge and find out that it is completely, utterly useless for its stated purpose. I've been through that -- I've also refilled my own cartridges with reasonable success. Having them refilled at Walgreens is by far the best way I've found yet for saving money and recycling this big chunk of plastic that makes my printer print.
At Walgreens they give you a cardboard holder, and an ink surface protector (I don't know what else to call it -- the blue thing in the picture). I've reused these three things (I think) three times. And the nice thing about this method is that the person who refills the cartridge does a test on them -- if they don't work you don't have to pay for it. You also don't get your cartridge refilled which means you have to either buy one new or root around your house for another empty cartridge.