A Great Online Textbook
Okay, so I found another online textbook (see entry below). This one is fantastic as it has both Prehistory - 1500 and 1500 to the present. Each course is broken down into the normal textbook categories. There are also great links which vary depending on the time period. The only glaring omission is lots of pictures, but if you wanted to save on a real textbook or need one for students to work on at home, then this resource might be the answer.

Digital World History Textbook
This is the only world history textbook I can find online. It is broken up into easy to follow subheading, has timelines and most importantly has a search engine.

A Brief History of the World
This source breaks up world history into its distinctive units and gives you (or your students) the essential points. It would be a good supplement for test review or a cumulative one at the end of the year.