Writing...Writing...Writing...Stuck.

My story got stuck. I've been writing it rather scattered all along, but now I can't think of things to fill in the gaps. It's turning out better than I expected and I'd say I'm almost halfway done with it, but now I'm faced with the same problem I'm always faced with. How to get from the intro to the ending. I should know better and not write anything out of order, but I think endings are my favorite part of stories so I write them better and I get them out of the way early so I don't lose momentum. That's a really bad idea, because now I have a good introduction, two or three chapters floating in the middle and a wonderful ending.

Now my question is this. How exactly do you get rid of writers' block?