There’s a deep grassroots "giving back" (or "paying it forward") movement sweeping the country. People across all age groups are volunteering like never before. But giving back doesn’t mean that you don’t get anything in return.Helping others rejuvenates us in ways that another margarita-soaked vacation, more stuff, a fatter resume, or a supersized house can’t begin to. We want to feel useful. We want to find meaning. We want to feel this alive and on fire with possibility. Here are some ways serving others can serve you--from finding your true calling to improving your health to boosting your overall sense of joy.