This is a WONDERFUL site for teachers. It allows you to put a bunch of different websites with a common theme together with your personal notes for your students all on one website. There is also a database of "tracks" already made by other teachers that you can use for your class. I have included the homepage and a track I have made about archaeology. My students LOVED TrackStar.
YouTube is great for teachers because there are so many educational videos in the YouTube database. Anyone can upload a video to YouTube, so as a teacher, I always watch the entire video clip for content before showing it to my class. My colleagues and I have also discovered that it is fun for us to get together to watch stupid clips after a stressful day. It is great if you are showing your students the Diet Coke and Mentos fountain experiment when teaching about chemical reactions or if you are de-stressing by watching a bunch of foolish guys from Alabama try to surf on surfboards tied to trucks in ditches full of water. I have included the YouTube homepage. You will have to search for the experiment (which is coolest if you watch the whole thing) and the Alabama surfing on your own. :)
OH, I thought of another one! MyCanvas lets you create books for FREE! I made a book of all of our photos from the year at the end of the year this past year. It is really neat because the parents have the option of copying the book to an account they create so they can add/delete pages and pictures (which changes the price). It is more personal than a yearbook. I would post my example, but two of the kids in the book do not have parent permission to be seen on the Internet by anyone but parents from our class.