Contact your local branch of Habitat for Humanity to see whether they accept windows. Habitat for Humanity locations that have ReStores sell used building materials, including windows, to the general public and use proceeds to fund building projects. Locations that don't have a ReStore may want to reuse the window in home projects.
Call used building material exchanges or salvage yards near you to see about selling or giving away the windows. Explore several options, then choose your preferred option and drop off materials to recycle windows.
Turn the old windows into a cold frame greenhouse for your garden. If you don't want a backyard greenhouse, contact school gardens, community gardens and environmental nonprofits to find someone who would be glad to reuse your old windows.