Google Related Links is a new Google Labs service that lets you add a list of related web pages and searches to your site. Unlike the homonymous service released by Google in 2006, the new Related Links restricts the results to your site.
"Related Links is a tool to help webmasters increase page views on their sites. Given a page on your site, Related Links can choose the most related pages from your site and show them in a gadget. You can embed this gadget in your page to help your users reach other pages easily. Related Links also suggests searches that users can run within your site to find even more related pages."
The service is not publicly available, but you can try a demo and ask for an invitation. "To apply for an invitation, please send an email to email@example.com stating your Gmail address, website domains and approximate pageviews per day."
Once you get the invitation, log in using your Google account and click on "Manage Related Links". You'll be able to configure the gadget, customize the look and feel and enable some advanced features: highlighting the keywords from the page for visitors that come from a search engine, blacklisting web pages from the list of related links and removing prefixes or suffixes from titles.
After configuring the gadget, paste the code in one of your sites and test if it works well. If you edit the gadget's configuration, the changes are reflected instantly and you don't need to change the code.
Here's a screenshot that shows the related links and searches for a post about Google Voice.
The results are relevant, but there are some issues which show that the service is still in an early phase: there's an encoding bug when displaying page titles and links are only opened in a new window.