Here are the best Web sites and references we've found for retirees who want or need to continue working. By Mary Beth Franklin, Senior Editor March 31, 2008 Stay active, keep learning and supplement your income, too. A growing trend says that more retirees are doing just this -- and lovin' it. Now is the time to rediscover your passion and put it to work for you. Here are a few resources to get you started:Best Web Sites for Retirement Jobs & Opportunities RetirementJobs.com Posts job listings in multiple categories for workers older than 50. Senior4Hire.org Lets you search for hourly jobs by zip code. Workforce50.com Offers job-hunting tips and job postings for workers who are 50-plus. RetiredBrains.com Links to jobs as well as volunteer opportunities at charities and nonprofit organizations. DinosaurExchange.com A job site for senior executives with an international focus. YourEncore.com A network of retired and veteran scientists and engineers who work for clients on a project basis. SeniorCorps.org Connects people age 55 and older with community-service projects. Bridgestar.org Executive search firm for the nonprofit sector. Recommended Books for Second Life Dream Jobs Portfolio Life: The New Path to Work, Purpose and Passion After 50, by David Corbett and Richard Higgins (Jossey-Bass, $25). Corbett is founder of Boston-based New Directions, a career-services company for senior executives. DonÕt Retire, REWIRE, by Jeri Sedlar and Rick Miners (Alpha, $19). Five steps to fulfilling work that fuels your passion, suits your personality or fills your pocket. Encore: Finding Work That Matters in the Second Half of Life, by Marc Freedman (PublicAffairs, $25). Freedman is founder of the Civic Ventures think tank. Test-drive your dream job: a step-by-step guide to finding and creating the work you love, by Brian Kurth (Business Plus, $17). Kurth runs VocationVacations.