When shopping for lemons and limes, look for fruit with the smoothest skin and the smallest points on each end. They have more juice and better flavor.
Lemons and limes will keep longer in the refrigerator if you place them in a clean jar, cover them with cold water and seal the jar well. After using half of the fruit, store the other half in the freezer in a plastic bag. This reduces the loss of moisture and retards bacterial growth. Properly refrigerated limes and lemons will last one to two months. Frozen fruit will last about four months.
-- 10,000 Food Facts, Chefs' Secrets & Household Hints