We are trying to develop a structure for an Intranet site on SharePoint but we don't know what items are a must-have for such sites.
For sure there must be News and Announcements. But what else?
If you're setting up an Intranet, I would highly recommend looking into the principles of Information Architecture. I've found O'Reilly's Information Architecture for the World Wide Web to be a fantastic resource (http://shop.oreilly.com/product/9780596000356.do); it's a fairly quick read and the first half of the book will grant you an immediate return on your invested time. The book isn't intended for SharePoint, but I've found the concepts to be very applicable.
The content and structure depends on what the end user wants. Below are some points you should consider
Once you collect these requirements, then you can translate those into SharePoint sites and content structure.