Now might be a good time to mention that you can still sign up at 52, a blog that encourages writers to write a poem each week, inspired by 52 different prompts. Many of these come from Jo Bell, who runs the blog, but there have also been a number of guest poets, including David Morley and, for the last week, myself.
I was truly staggered by the enthusiasm of the response to my own prompt, by the quality of the poems that resulted, and by the willingness of the participants to offer constructive criticism to their fellows. A number of poets produced several excellent pieces of work, and several more who said they'd found the prompt difficult managed to come up with some superb work, proof perhaps that the best poetry has to involve a little bit of pain in the writing process. There are a number of much-published poets on there, as well as beginners and everything in-between.
So, if you fancy giving it a go, take a close look - you can always catch up on the older prompts as you go along. There's a closed Facebook group linked to it, which you're invited to once you join.