Hebrews 11 list a number of people that Hebrews 12:1 calls a "great a cloud of witnesses". Among them are the usual suspects: Noah, Abraham, Issac, Jacob, Joseph, and Moses. But there are also some lesser names, including Abel, Enoch, and Rahab:
By faith the people crossed the Red Sea as on dry land, but the Egyptians, when they attempted to do the same, were drowned. By faith the walls of Jericho fell down after they had been encircled for seven days. By faith Rahab the prostitute did not perish with those who were disobedient, because she had given a friendly welcome to the spies.—Hebrews 11:29-31 (ESV)
Joshua 2 gives an account of how Rahab welcomed them. (By the way, there's little evidence she offered them sexual favors.) She was afraid for her life because of the Hebrew's military victories and betrayed her home town when she hid the spies. Is that really a sign of her faith? Why isn't it the spies that are honored? Why was Rahab listed?