I’ve gotten writing prompts from the following websites.
The Daily Post’s Daily Prompts (WordPress)
The One-Minute Writer on Blogspot.
More writing prompts can be found on Daily Writing Tips’ Writing Prompts 101 web page.
Reddit has a writing prompts page.
Tumblr has a writing prompts tag.
Toasted Cheese has a writing prompts calendar.
Ryan Lanz publishes unique writing prompts once a week on his website.
Dragon Writing Prompts is a good web site if you like to write sci fi/fantasy.
Creative Writing Prompts for Writers has writing prompts for dystopian, horror/thriller, fantasy/science fiction, and other subjects.
If I find any more writing prompts, I’ll post them here.