Last week, I was talking with a friend and could not think of something I wanted to write about for Cheff Salad, so I asked him to give me something to write about. Being a smartass, he said, "x-rated pasta." And always being up for a challenge, I accepted.
I find the challenge of a writing prompt is really good for sparking some creativity. What's interesting to me is that the creativity was two-fold that night. Not only did I write for the challenge I was given, but I also happened to come up with several ideas that were added to my ideas list (including this one).
If you ever find yourself stuck and you just can't motivate yourself, then get help from somebody else. Tell them to give you something to write about and don't complain about whatever it is you get. Take it on and do something great.