Paint has a long shelf-life. It is still usable as long as it mixes smoothly and isn't lumpy. Try to buy only what you need and share any that may be left-over with friends, family and charitable organizations. The transfer station will accept paint for recycling. Please see disposal fees for rates.
You may also dispose of left-over paint by following these steps: Locate a safe, dry area outside - away from pets and children. Remove the lid from the can and allow it to sit until dry. You can speed up the drying process by pouring the paint into a bucket or box lined with plastic and mixing it with kitty litter, sand, sawdust or shredded newspaper. When dry, the paint, cans and other materials may then be safely disposed of with your garbage.