Summer's such a good time to change it up in your writing, experiment, push yourself. Because it's going against the grain already, just to be writing in summer, let alone challenging your muse to give it up. Karen Weyant has an interesting exercise at Scrapper Poet from her "jailbreaks" workshop. ReadWritePoem is always good for a jumpstart - this week's is Fun With the Dictionary.
Word lists seems to be popular prompts, so of course I've written a poem about word lists. I was always a bad student. I would take an exercise, stand it on its head, turn it into a poem or play and present the result to the teacher. If it were a multiple choice test I would make a prose poem out of it. I should write The Rebel's Guide to Better Grades. They always gave me A's because they had no idea how to comment on what I had done. But if I wrote that book, all you parents would have to hate me. All of this bad student history is in my memoir, Rocket Lessons. If anyone knows of a publisher interested in a bad attitude rocket kid, let me know.
And of course, childhood, as Rilke said, is a great touchstone for poetry. Here's my prompt: write down five confusing things that happened to you before you were nine. Pick two and combine them in a poem. You can do the same with five awful things, five surprising things, etc.
Speeding you the Muse!