Save your pop-tops. Either store alongside the used cans or have a separate bag for them, if you want to give them to charity. Remember to rinse sticky drink residues from the cans and the tops, to avoid attracting pests.
Locate your nearest recycling centers; nearly all accept aluminum and some pay. You can find addresses through Earth911's search function.
Contact the recycling centers if you are planning to sell your aluminum. Some centers may offer a better price than others. If you have a lot of aluminum, perhaps from a community collection project, a scrap metal dealer might offer a better deal.