Google overview of Google Sites -- see the page for more details, screen shots, etc.
Google Sites is the easiest way to make information accessible to people who need quick, up-to-date access. People can work together on a Site to add file attachments, information from other Google applications (like Google Docs, Google Calendar, YouTube and Picasa), and new free-form content. Creating a site together is as easy as editing a document, and you always control who has access, whether it's just yourself, your team, or your whole organization. You can even publish Sites to the world. The Google Sites web application is accessible from any internet connected computer.