I'm still on my way back from Las Vegas. While I was gone, Rachel Mckibbens (whose own prompt blog is on the list of links to the right):
A “ghost line” is a line you use to prompt or inform a poem, but erase from your work at the end. You can use a ghost line of your own devising, from daily life, or borrow one from another artist.
Try starting your poem with a ghost line: delete it when your poem has taken shape. Here’s a possible example from Jason Carney’s (who has also featured while I'm on the road) Starve the Vulture:
Faith without work is dead.
Write Or Die
Scott Woods's Twitter Prompts
Rachel Mckibbens' Prompt Blog
The 30/30 Prompt Blog
Asterisk And Sidebar Prompts