Google has a plethora of tools available for teacher use. They are all free. One of the most popular is Google Earth there are many videos available to show you how to use this great tool in your classroom.

Here is one really good example.

I also like Google Squared - if you want to search for a broad topic, say Australian Explorers, you can put the search term into Google Squared and it gives you a grid ('square') of the items it found. You can then refine your search by deleting any that you don't want and adding columns to further refine the search.
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Another excellent use of Google Apps is to use GoogleDocs where you can create and share documents online with your team or class. You can allow others to edit these documents making them a great way to collaborate in class.
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Google+ for educators slideshow.
Google+ is the new version of Google tools. It includes Circles,spaces to drag and drop information and post to particular groups set by the user, Sparks, a news feed that is customisable and Hangouts, a video chat interface where groups can get together. There is an in depth how to here from the wonderful people at Read Write Web. As it is very new, you have to wait for an invitation from a current user. I am currently testing it, so if you are interested leave a message on the message board with your email address. You need to organise to have a gmail account if you wish to use it.

Google Docs- How To Sheet