There are many useful videos on World War I on YouTube. The video below comes from the outstanding The Great War series; you will find more videos throughout this guide.
The History Channel - World War I
This comprehensive resource covers all aspects of the war, the only thing missing is an Australian perspective.
The Guardian Newspaper - WWI Interactive Documentary
If you only visit one website - this should be it! It explains the events and conditions leading up to war and all events, battles and so forth up to the aftermath of the war. This website allows you to explore at your own pace and includes primary resources from the time period.
ABC News - Australia Remembers WWI
For a perspective that focuses on Australia's involvement visit this excellent site. It is also interactive and includes such features as a timeline of the main events and videos.