How do you stay motivated?

So you've started a new story. It's all fresh and new, and you can't stop thinking about it. Your characters are really coming to life, and you are really beginning to care for them. You're cruising right along and then BAM! You lose interest.

I really don't like it when this happens to me. I'm not exactly sure what sparks this sudden non-desire, but my hard drive is riddled with abandoned stories.

I've found that when it really counts and I have to finish the story, I'll find pictures of what I think the characters look like. I'll either cut them from magazines or find them online. Having a clear idea of who they are, and then having them staring at me is really motivating. Or, if I've based the characters loosely on someone I know, I'll either visit or find out someway (Facebook) how they are doing, thus piquing my interest again. These are odd little quirks - I know - but I'm pretty much a visual person, so having either the storyline, images, or even just the list of characters in my face, helps me focus.

Does this ever happen to you? What makes you move on? What keeps you from abandoning your wip - other than a concrete deadline?