There's a blooming trade for domain names on the Internet, and many people make extra money buying domains and selling them for a higher domain price to an interested buyer. There are many ways of selling a domain name easily.
Using a broker site
There are websites that specialise on the buy&sell domain business. They put in touch buyers and sellers, and receive a share on each closed transaction. It is often free to put your website domains up for sale.
How do you auction your domain successfully?
You can list a full website or just a domain, but the key to selling it is proving its value. There are several ways of doing this, from having statistics about the visitors to being able to explain the potential of a keyword rich domain to a potential seller. Most people who resell domains professionally choose to create a very simple website to get some traffic statistics, and increase the domain price. Some auction sites will offer this service, called domain park.
Advertising your site yourself
If you don't want to pay commissions to a domain auction site you can also advertise the domain name yourself. It's important to keep in mind that you will need to take measures to protect yourself from those who intend to scam you or forget to pay after the domain transfer is complete.
On your own website
If you intend to sell a website you own, including the domain, the best way of doing that is advertising that on the website itself. You may find that one of your existing subscribers wants to take over, and it's considerably easier to show the potential of your website to somebody who is already acquainted with it. Using a domain forum
There are forums and classified websites dedicated to buying and selling domain names. They often sell associated services, such as a escrow service to keep the money safe until the trade is complete and the domain details have changed. You can place a link to your website and your starting price on those forums, often for free, but they won't manage your communications with your end buyer as a domain broker would do. Many people also post requests for domain purchasing, stating the kind of domain or website they are interested in buying, so it may be worth taking a look at that as well.