Been there. My best ways to deal with it is read something else, write a story in a completely different genre or write a "deleted scene". With deleted scene, I mean scene with one or more of the main characters you have no intentions in putting in the story. I was a bit bored of my current book, so I wrote a long scene with the two main characters going to the movies. It doesn't make sense storywise, but it was fun to write and let me get to know the characters bit more. I even wrote a.... dirty... scene, but it won't be published anywhere.
Don't most writers drink heavily at that point...? Seriously, though, do something to get yourself inspired. Take a sudden trip to a foreign country. Drive somewhere far away and go backpacking. Buy a couple of tickets to a concert sixteen hours away, find a few friends, and head off for a weekend-long trip into insanity. Fall in love with someone who lives as far away from you as possible. Find some object or garment or bit of armour from history that you find intriguing and replicate it. Take up pipe smoking. Wake up before dawn every morning to go running. I've done all these and more at various points in my life, and even if I did not realise it at the time, everything served to have an effect in my writing later on. Remember that your best pieces of writing will probably be those where you are drawing on some life experience, in one form or another.
I usually grab a glass or two of whiskey and then talk to my Muse, if I get the chance. After a week, I'm back into the proper perspective.
Okay, where's this "writers drinking heavily" coming from? Still, I was hit by the biggest wave of muse when I was in Philly a few years back exploring its history. Maybe I need to go back there...
