By parking your domain name to the DNS servers of 'domain parking' companies you can earn an extra stream of income from visitors who access your URL.
Simply register with a domain parking company such as NameDrive and redirect your domain name to their servers. When someone visits your URL be it from a search engine, a link on another site or a direct type-in, they will be shown a page of search results relating to your sites domain name and/or previous contents.
Each time a surfer clicks on one of these sponsored links you earn an income, similar to using any other Pay Per Click search engines or publishing networks.
An example of a parked domain is: http://www.eGoldJobs.com
May domain parking sites offer payments by PayPal and accept members from around the globe. So if you have a domain that is sitting around doing nothing, and you want to get something out of it - park it!