Write or Die was a site that I stumbled upon two years ago after my first NaNoWriMo venture. While I was a little disheartened upon finding it that late (since I thought it was a good productivity tool), I had kept the site in the back of my head for the next NaNoWriMo, which was last year. Needless to say, the site helped me a great deal in cranking out a few thousand words in a day, which is something I don’t usually do.
For the uninitiated, it pretty much prods you into writing. The tagline for the site is “Putting the ‘prod’ in ‘productivity,'” and the site does not fail at that. There are four “modes,” which–depending on how much you plan on writing in a certain amount of time–may either clear your writer’s block and force you to reach a part of your novel that you haven’t even considered before, or leave you tearing out your hair in frustration. The four modes are Gentle, Normal, Kamikaze, and Electric Shock. Along with the modes are three “grace periods”: Forgiving, Strict, and Evil. I have only tried “Normal-Strict,” I’m too paranoid to go any further than that, haha.
The consequences vary from a small pop-up that reminds you to write, to a highly annoying sound in your ear (which stops once you start typing), to an extreme form where your work starts deleting itself. Of course, once you reach your goal (which you can set) in the amount of time that you set, you are free to wait out the rest of your time, or you can add more to what you have already written.
I highly recommend this site not only for periods when you are stuck or suffering from writer’s block, but whenever you write. There is also a desktop version that has a few extra features (one of which includes saving what you’ve written) that is $10. If you have the spare money, go ahead and download the desktop version.
Let the Muse Shout! 
Sounds interesting and a bit annoying, as you say.
It is rather annoying, especially when you’re listening to music while you write. But I think it basically “annoys” you to your goal, and pretty much helps you get the job done that way.