AceShowbiz - Stars including Alicia Keys, Sir Elton John and Whitney Houston have offered themselves up to the highest bidder to raise money for a human rights charity. Justin Bieber, Gwen Stefani and Oprah Winfrey are also among the celebrities donating their time for a 'meet and greet' which is being auctioned off online to benefit the Robert F. Kennedy Center for Justice and Human Rights.

Other lots include the opportunity to spend a day on the set of John Cusack's new movie and a signed hat worn by Harrison Ford in the "Indiana Jones" movies. Kerry Kennedy, founder of the RFK Center's Speak Truth to Power campaign, says, "By bidding on these incredible experiences, people will be supporting cutting-edge human rights defenders from around the world, including those fighting for the right to water and reconstruction in Haiti, the peace process in Darfur, farmers' rights in the U.S and much more."

Bidding on the items ends on April 28.