It is estimated that more than 500 URLs have been bought and sold for $1 million or more.

We scoured domain name resource DN Journal and put together a list of documented million-dollar, domain-only sales. Some have been squatted on for 20 years and have only recently traded hands.

Not surprisingly, sex- and gambling-related domains are some of the biggest money makers.

Below, check out the most expensive domain names of all time.

Note: Web businesses have other assets and are not domain-only sales, so they were not eligible for this list. For example, Insure.com was bought for $16 million as a fully-operating, profitable company. DN Journal reports only the domain names sold after 2003 because prior sales are not verified by credible sources. 

MM.com — $1,200,000

Date sold: July 2014

MM.com was sold for $1.2 million through Sedo in July 2014. It was purchased by Hangzhou Duomai E-Commerce Co. Ltd, a company behind other domain names Game.com, JZ.com and 4.cn.

eBet.com — $1,350,000

Date sold: October 2013

A man named Rick registered eBet.com in 1996 and held onto it until September, when he agreed to sell the domain.

"Network Solutions contacted me on August 29th with a $50,000 offer. I did not think anything of it, as I get these all the time," Rick wrote on his blog. "I countered at $1.8M and went about my business. On September 3rd voila the buyer comes back at $1MM ... So I think, how to get that number where I can live with and at the same time they can live with. So I counter at $1.35MM and that was my final offer. I hear nothing until the following Friday. September 16th. They accept the offer!"

Cameras.com — $1,500,000

Year sold: 2006

"Cameras.com attracted the highest bid in the live domain auction conducted by Moniker.com at the recently concluded T.R.A.F.F.I.C. East Conference in Hollywood, Florida," The DN Journal wrote in 2006.

"The winning bidder, Sig Solares (the CEO of Parked.com), wasted no time ponying up the $1,500,000 due, making that domain the first from the live auction that we have seen change hands."

Russia.com — $1,500,000

Tandberg.com — $1,500,000

Year sold: 2007

"Tandberg Data, a leading global supplier and manufacturer of backup and archiving solutions, decided to take the cash offer for Tandberg.com from Tandberg, a leading global provider of visual communication products and services with dual headquarters in New York and Norway," The DN Journal wrote at the time of the sale.

The deal was actually completed in December 2006 but wasn't made public until early 2007.

Ticket.com — $1,525,000

Year sold: 2009

Ticket.com raked in a lot of cash for Afternic.com when it was sold off in October 2009. BuyDomains brokered the transaction.

DataRecovery.com — $1,659,000

Year sold: 2008

Minnesota's Associated Computers Inc. sold the domain to ESS Data Recovery on Feb. 1, 2008. ESS had been trying to buy the domain for a long time.

Auction.com — $1,700,000

Year sold: 2009

Auction.com was rumored to be selling for even more money — $2.5 million. But it came in at $1.7 million after being purchased by Real Estate Disposition Corp.

Dating.com — $1,750,000

Year sold: 2010

Dating.com was acquired at the at DOMAINFest auction in Ft. Lauderdale, Florida, in May 2012. The next-highest domain name to go at that auction was Boardgames.com, for $450,000.