I struggle with middles in my longer writing projects. I'm always excited about the beginnings (isn't everyone?). And at least some of the time I'll have some good stuff queued up for the ending, so I know how that's going to look. But the middles catch me and drag me down. I have stopped writing in the middle of a few too many wannabe novels.
This podcast from Writing Excuses addresses middles and has some great advice. I especially like the conversation about try/fail cycles and also predictability.