Available on your iPhone or iPod Touch, the app allows you to book, confirm, and check-in for flights, while its new "Ding!" feature immediately alerts you to any new and upcoming airfare sales so you can get the most bang for your travel buck. Plus, you can book car rentals, get flight schedules, and redeem your Rapid Rewards points. Great for people who love to take advantage of cheap fares, maybe not so great for those workaholics who never take vacations. PS — you should do that more often.