So, I can't be the only person who thinks of random prompts for people (to get the juices flowing) that don't actually fit any "challenge" threads. So that's what this is - a thread specifically for random prompts. Hopefully some prompts are useful for someone. I'll get us started:
You're sitting alone on an island beach.
You're inexplicably afraid of the last thing you ate.
Turns out, Star Wars is real!
Your significant other has been possessed by a character from a kids' TV show.
"I never knew why,"
says the sock puppet of rage.
"I might never know."
(Perhaps keep things to 5 prompts per post?)
Go! 
Radishs are on sale for 50 cents off and you have to beat rush hour traffic to get to them before they sell out.
Rubber chickens come alive and slap back.
The narrator thinks of various vehicles fit to destroy the lines at drive-thrus.
The greatest possible day of your eternity.
Secrets buried deep within your couch cushions...
Facing Winter
Recovering
Sliding Into Darkness
My Last Chance
The Flowers Come Back Every Spring
Externally Yours
You wake up missing one number in the lottery, you know the blue unicorn has it tattooed on a hoof and he is at the end of the double maze. Pick a team and find it!
Struggle Bus
Insectoid Queen
Patient Zero
Last Christmas on America Street
The Predators Ball
Month of Sundays
Which species would you annihilate to make Earth a better planet?
Which already-extinct species needs to return to help heal Earth?
Write about the most inebriated you've ever been (any substance).
You just bought your dream instrument. What's the first song you write with it?
Things Of Old
Matter Of Dreams
Reach For His Own Way
Kiss Her Dance
Woman Circus
Golden Circus
Sweetie, Wouldn't It Be Nice
Darling, Sing With Me
He heard He's Trouble
She Hopes We Know
See You In The Shadows…
If I could change one thing...
Getting back at my bully...
I've run out of peanut butter....
When will the sun come out?
Gotta get that out of my life....
That song reminds me of...
You sow what you plant....
Recurring Dreams
Yard Sale Jingle
Worst Date Story
Food Poisoning
My Utopia
Desert Blues
Don't Panic!
Caligula's Table
I Never Knew Why
Soap and Other Poisons
Use the title of any thread from the forums.
Turn to page 53 of the closest book.
Try to play what you think your favorite song would sound like backwards.
Write about the contents of your pockets or purse.
What is the first thing you did this morning? Write about how someone much cooler than you would do the same thing.
Follow someone around and write down everything they say.
What would be your last thoughts while falling from a cliff?
What is your favorite thing you can make other than songs?
Sorry for the errors, you would not believe how hard it is to type and edit posts on this thing. [Edit: I went in and fixed them on my computer.]
Fella, Take it Outside!
@Candle here is my take based on your title "Matter of Dreams". Thanks for the inspiration! http://fiftyninety.fawmers.org/song/47258
Synthetic Sympathy
Drama in the Playground
Demons and Rayguns
Dragon Restaurant
Demands of Ratqueen
These are all misreads of the spine of a book I can't quite make out from here.
Write a song dedicated to the most striking person you saw last time you went to the shops.
Play the instrument you use the least as if it was your go-to instrument. Try to make it sound as similar as possible.
is there a surface covered with random stuff somewhere in your house? Good! Sit down in front of it and use all the stuff as your instruments.
Make up A genre then make up a band in that genre, then become them.
Figure out what Noises you make most in your everyday life, then use them as the basis off a song.
analyze the rhythm of A repetitive task, like folding laundry.
Ask someone for A silly song prompt, then write a very serous song about it.
Write A song about what you look like to strangers, too close friends, and to yourself.