The domain name, sex.com, just sold for $13 million dollars. It was sold because the former owner, Escom LLC, went bankrupt. It was offered through sedo.com, a large broker of Internet domain names, and instead of being sold at auction, it was sold as a negotiated sale to a company called Clover Holdings, based in the Caribbean island of St Vincent. The domain name reportedly sold for $14 million a few years ago. Gary Kremen, the founder of Match.com, was the one who originally registered the domain back in the 1990's.
This domain name has had a notorious history, including being hijacked through identity theft, and Kremen spent a long time in court getting it back. You can read all about the history of the domain in the book Sex.com: One Domain, Two Men, Twelve Years and the Brutal Battle for the Jewel in the Internet's Crown (Volume 2) and the book The Sex.Com Chronicles: A White-Hat Lawyer's Journey to the Dark Side of the Internet.
Don't forget to check out the Top Domain Names are Owned by Publicly Traded Companies.