Wordcloud creators are very popular tools for educators. I have long been a fan of wordle and have used in many times to create pre-reading images, brainstorming activities and various student projects.
Another service, Tagxedo, adds an interesting feature: using shapes for your word clouds. It’s really easy, and you can simply download your creations.
I recently read some Konkrete Poesie with the students in my German writing course, and then had them write their own.