My overall favorite way to get myself going again is through prompts. Here's a list of sites I've used (some we've even used here on AuthorCulture for our writing contests):
Archetype Writing's Plot Scenario Generator, Character Generator, and Everyday Problem Generator (because "nobody's life is perfect").
I particularly like the problem generator. The one I landed on when getting the link was: "Your character has problems with impatience, is afraid of dependence on others, and can't stand meeting new people. Also wishes the world were free of witchcraft."
Dr. Wicked's Write or Die is an evil little devise that punishes you if your fingers stop pecking the keys. Everyone has to try this at least once. It's great for free-styling.
Dragon Writing Prompts throws visuals into the mix. For interesting variations, look through the Categories listed in the sidebar.
Andrew Bosley's Brainstormer is a roulette style wheel where you can mix and match theme, setting and character. (Andrew has also developed an app for this. See our right sidebar.)
Creativity Portal has a great list of sites that provide writers prompts, grouped by prompt topic, and The Book Chook has a list of sites designed to get kids interested in writing.
Of course, a good search can produce a boatload of prompt generators and sites, but don't waste too much time going through them--you're supposed to be writing!