I love writing prompts.  In school, I looked forward to the journal writings we did, just because it was five or six minutes to be completely creative, and not have to worry about structure, or form, transitions...none of that.  But when I wanted to do some creative writing outside of school, it was harder without a prompt.  Aside from there being countless sites online, I'll throw some of my own out.

1. Look up a new word in the dictionary.  Write anything about that word that comes to mind.
2. Take the last line of a poem or song, and start a creative piece with that line.
3. Write about your perfect place.  It can exist, or be made up.
4. Think of the hungriest you've ever been.  Write about how it felt.
5. Write a letter to yourself at a different age.
6. Take the most boring day you can think of.  Write about it, but make it exciting without changing the events.
7. Put two of your favorite characters of any sort together in a room.  What happens?
8. Write about your favorite simple pleasures.
9. Flip through an old photo album, magazine or newspaper.  Write about the first picture that draws your eye.
10. Even more fun, take out an old yearbook.  Pick a random person and write what you think they are doing since you last saw them, even if you didn't know the person.
11. Write a letter to someone that you would never send.
12. Listen to a TV show.  Take the first line someone says, and write, putting that line in the writing somewhere.
13. Pick a profession.  Write what you think a typical day in that job might be like.
14. If you had to spend the rest of the money in your bank account, what would it be, and why?
15. Imagine you didn't bathe for a week.  How would friends, family, coworkers, etc. react?
16. List your biggest pet peeves.  Pick one and write about it.
17. Pick an inanimate object in the room, and write about that object's daily "life".
18. Write about a mysterious cab driver.
19. Imagine something that could make you blissfully happy.  Write about it, and how you could achieve it.
20. If you could meet any historical figure, who would it be and why?

Hope this was helpful...remember, searching for these sites online will give you practically endless prompts!  Good luck writing!