I love Popplet for supporting writing, creating diagrams, timelines and mind maps. This is a very flexible tool. Once your popplet is complete, you can save it to the camera roll or email it as a jpeg or pdf file. Note that popplet.com is also an online web 2.0 tool. With the online tool, you can collaborate and embed videos. You must use the app on the iPad.
There is a FREE or lite app and paid app. The free app suffices with only one popplet to work on at a time. This means that you cannot have multiple popplets in progress on an iPad, but must complete and save the popplet to the camera roll before beginning a new one. It may be worth the $4.99 for the full version with unlimited popplets editable and saved.
Kinders in Matt Gomez' class map adjectives
First grader plans his paragraph on his pets
Second graders in Ms. Widen's class map the beginning, middle and end of a story
Middle School Spanish Vocabulary Made with Popplet.com (Flash-based, can't view on the iPad)