If you've recently purchased a new printer, you might have some unused ink cartridges lying around that you can't use anymore. Rather than selling them or throwing them away, why not donate them to a worthy cause? Ink cartridges are expensive, and there are many people and organisations that would love some free ink. By donating these ink cartridges rather than tossing them, you will be getting rid of your clutter and helping someone else in the process.
Check with local institutions. Libraries, schools and hospitals go through a lot of ink cartridges and could certainly use the donations. Call these types of organisations and ask if they have a compatible printer.
Offer the cartridges online. Freecycle is a website that allows you to swap useful items you have. You could exchange the ink for something else you need or just give it away outright. Craigslist has a "free" section on their site where you can offer free items for the taking.
Ask your neighbours. Ink is expensive, and someone around you might make use of a free ink cartridge. Ask your friends and neighbours if they have a printer that uses the type of ink you have.
Donate them to a local charity. Many charities take any items you have to donate and sell them to raise money for their cause. Use a search such as Charity Navigator and contact local charities to see if they can use your ink.
When posting an ad on Craigslist, never put your address directly in the ad. Wait for an e-mail from an interested person and then offer to meet them to give them the ink.