Not enough prompt ideas yet? Really? Well, here's another thing you can do. You can use tarot cards to plot a story. You don't have to spend money on it. You can just go to a free site like Facade.com and cast the dice, so to speak. There are all kinds of fortunetelling tools there--maybe you like runes instead. Anyway, you don't have to use these things to foresee your own future, you can plot your characters' as well.
Facade.com isn't too keen on people reusing their images, but I can say that the Twisting Path spread might be a good place to start. It's about a couple of choices ahead and a couple of pitfalls. Just what any good story needs.
I'll also point you to Seventh Sanctum again, where their latest project is the Science Fiction Tarot Card Generator. This deck could come in handy if you're writing a tale about technology or the near future.
The Empress of Mutation? The Ten of Time Tunnels? Come on, it doesn't get much better than that.