Freeze it. As long as you use a good quality airtight container it will last months. I've got a container of it in my freezer that I continually add to, everytime I buy a lemon to use in a recipe I'll zest it first and usually put at least half of it into my zest stockpile. I never run out, it's fantastic. Don't get freaked out by the little ice crystals that form on top, that's normal.

I remember reading you can dry it out in a low oven as well (just found the link: http://chocolateandzucchini.com/archives/2010/06/roasted_lemon_zest_powder.php), been meaning to try it but haven´t got around to it. You could do as she suggests and stick extra peel in the oven anytime you´re preheating it for something else. Or you could make candied rinds (though you´d need a large quantity of peel over a short period of time for it to be worth it).

Why not just dry it by spreading it out on a plate and leaving it overnight? It does lose some flavor, but it's better than commercial dried orange peel, and there's always a use for it -- just throw some in your pancake or muffin batter.

You can also zest the citrus, then squeeze it through a piece of cheese cloth or a lemon wrap to extract the oil, then freeze it. Citrus oil has a fresh, bright flavor when used in uncooked recipes, like adding to just made chocolate ganache instead of cooking it in the cream, or into mousses or in salad dressings etc. Lime oil is very hard to get any oil out of, since the zest is so thin and dry, but it's worth the effort. Grapefruit, lemon and orange oil are all great to work with.

You can freeze it as people said above. But you can also extract the juice, and mix it with the zests, put everything in ice cube trays. Once everything is frozen, pop the cubes inside ziplog bags. I keep them for 3/4 months that way.

Two recipes from the Kitchn I just made this week with lemon zest -- blueberry and lemon muffins and the braised spinach and chickpea coconut milk curry. You could maybe store the zest in a bit of olive oil for a nice salad dressing? Or in ice cubes for gin and tonics?

I like to add lemon zest to pancakes--you can't really tell that it's there, but the pancakes are sooooo much better tasting.