I liked Phoetic more than a regular word cloud but until today I hadn't seen something web-based that does this same thing. Hesitant to make students buy an additional app midstream, we discovered Tagul.com. Here's Tagul in action:
It does the much the same thing as Phoetic and it's free. I've used WordClouds and Phoetic in teaching for several years. I've used it as an anticipatory set, I've used it to teach metaphor, and I've used it as a part of a larger project https://goo.gl/GpAOvi. To see other ways to use word clouds in the classroom, check out this post from edudemic. If you want to go the word cloud route there is Wordle- though it won't work on an iPad. This morning, we also discovered worditout.com.