1.
Use it on something or give it away to somebody else who can use it.
I have many gallons of perfectly good paint in my basement and occasionally I will come across a job that I could use a good bit of it up on, or, a family member or friend will have a project that they will need some paint for and I can help them out.
2.
See if a local production company or school would want the paint as a donation to their arts/production class.
Many schools need paint donations to create scenery and backdrops for their school plays and art shows.
3.
For many municipalities around the country (including mine) you are allowed to throw away old paint in the trash as long as it is no longer a liquid.
The paint has to be dried out completely before you can throw it away.
There are several ways to dry out paint quickly.
If you have an empty corner of your garage, shed, or a dry basement, then you can simply take the lids off and wait for them to dry out.
Other options are to mix old kitty litter or sawdust into the paint, this will dry them out very quickly.
Always be sure to find out what the local rule is about disposing of paint.
Usually your local paint store should be able to give you direction in this matter.
4.
Pay to have it disposed of at dump as toxic waste disposal.
Paint is really not that harmful to the environment (especially newer paints) since most of the ingredients in paint come naturally from the earth, however, dumps will charge you and arm and a leg to dispose of it.
5.
Take off all labels and manufacturer identifying features from the can, put a dot on the lid to show what color is inside, then sell it at a flea market or yard sale.
People are always happy to get decent paint at a low price.