Web tools are built around the concept of Web 2.0. Web 2.0 is the term given to describe a second generation of the World Wide Web that is focused on creating, collaboration and sharing information online. It is an umbrella term for recent applications such as social networking, social bookmarking, blogs, wikis, multiplayer online gaming etc.
There are so many web tools that maybe useful for teaching that it would be hard to include them all.
Below are a few of my favourite Web Tools:
I love 'Wordle' a great way to make 'Word Clouds' (see above) which you can then use in your presentations or web pages. http://www.wordle.net/
An online wall that allows collaborative post-it note activities.
This site allows you to easily brainstorm and mindmap online.
This social bookmarking website allows you to access your bookmarks anywhere and share with others.
Beyond the Basics
If you are looking for new WEB 2.0 tools or evaluating any technology for the classroom these two websites by Richard Byrne are a great starting point.
Favourite Tech Resources for Teachers
Free Technology for Teachers