When I make salsa, I use half a bunch of cilantro. For a while, I would just let the extra go bad in my fridge (BAD IDEA). Then I realized that I can easily dry out the remaining cilantro and use it that way!
Preheat oven to 250-300 degrees F. Lightly coat a cookie sheet with baking spray to help with sticking. Strip the leaves off the stems of the cilantro, and spread the leaves in one layer on the cookie sheet. Let the leaves dry out in the oven for 20 -30 minutes, check once. You just want the leaves to lose the fresh green look. Take them out of the oven and cool on the cookie sheet. Use a spatula to scrape off the cookie sheet, and slightly crumble the leaves. Put in an airtight jar and store with spices, use when needed! These will last as long as any other dried herb you buy.