Scratch is a free, easy to use, web app from MIT that allows students to create basic programs using a visual interface. Students can program animations, games and videos by dragging blocks together. Each block represents a function and snap together to create the program.
It is a great tool for teaching students basic programming logic and processes.
There is a huge community of users and plenty of shared examples to learn from, as well as an Educator Resource page.
Here is a video explaining it more: http://vimeo.com/65583694
Here is an example showing the programming blocks:
Google Blockly - easy to use visual programming language