1. More Etherpad replacements - This was touched on a few weeks ago with Primary Pad and Typewith.me, but more and more Etherpad replacements keep popping up. Here are a few more.
TitanPad - TitanPad has the same interface as you would have seen with Etherpad, which is the same interface as Primary Pad and Typewith.me. You can instantly create a public pad for use and a random URL will be generated. You can invite others to work on the real-time document with you and see their edits as they type. Like the others, it does not save automatically, so make sure to periodically press "Save" so your work does not disappear. You can view old saved revisions and use a slider to see how the document developed over time. Before leaving the pad, make sure to copy the URL so you can return to the document at a later time, or export it in one of many formats (HTML, Word, Text, PDF, etc.).
Sync.in - Sync.in also has the same interface as you would see with the other Etherpad replacements, although it has more of a Web2.0 look and feel to it. There is also a pro account ($2 per user per month) where you have a little more control over who can access the documents, as well as search and filter through them. There are also fewer options for exporting and no importing options as you would see in the other replacements. (Shared via @ozge on twitter.)
As time goes by, there should be even more Etherpad replacements that arise, as the source for Etherpad has become open since (obtain information here) being acquired by Google. You can view a listing of many through etherpad.org.
What Should I Read Next? - Many times, teachers really struggle to get students to read for pleasure with all of the other options available to them (TV, internet, video games, etc.), so when you get a student to start reading, you want to keep the momentum going. But what should you suggest for them? What Should I Read Next is a site that will help you (and your students) find more books that fit any reading style. You can search by book title, author, or ISBN. For example, I just finished reading The Lost Symbol by Dan Brown, so I did a search for that book and received this list of books I might enjoy. On the list, I can click on the American flag, and I am taken to Amazon where I can check the summary of the book and purchase it if it catches my fancy. With students, you can use this tool so they can find recommendations for books to sign out of a library. (Shared via Michelle Krill on Diigo.)
3. Astronomy Picture of the Day - NASA posts one picture each day with an explanation as to what it represents. Links are provided to give further explanations as to what specific concepts are. An archive of previous photos is kept, as well.
Working with these photos could be a great warm up for a science class to discuss to science behind the photos. In a language arts class, the photos could be presented to the class with a short writing prompt to open up creativity and a connection between science and language arts.
Photos are archived the whole way back through June of 1995. As you browse the older photos, you will notice a difference in the quality of the photos. This could lead to a discussion of technology and how it has progressed through time.