Neil Gaiman recently posted an essay about the dreaded question writers get asked frequently: Where do you get your ideas? I don't find this question all that annoying--or at least not yet. Mainly because each one of my ideas has a bit of a fun story behind how it came to be something I wanted to write.
Human Dignity: Ethics class run amok, and I mean amok.
The Masque: Writing exercise supposed to get you thinking about the masks your character wears and what your character might do with a mask's annonymity; I chose to write about what a Masque Ball might look like in the future, and on Mars. Then other story ideas generated by a line of dialog and watching SG-1 sparked the rest of the Masque Universe.
Princess Incubus: Someone at a con read a story from the POV of a succubus's victim. I spent the entire time wondering what the story would sound like from the succubus's POV. Decided to write it.
Strings of Betrayal: While driving between Grand Teton and Yellowstone, I happened to look into a glade that was bordered by aspen and pine trees. I saw a vision of a ephemeral creature stand in front of the aspens and vanish into the darkness of the pines. I knew there was a story there, and I've spent the past three years hunting it down.
I love sharing these stories of how my ideas came to me. Mainly because then I get to relive those moments of discovery, those instances of "Wow, that's something I've GOT to write" or "There's something cool going on here, and I'm going to find out what". That first spark is amazing, and I don't think I'll ever reach the point where I won't be willing to share the story of how I got a particular idea. But if someone just wants a general idea of where all my ideas come from, I'd have to make some vague gesture to the world and my head. I don't get all my ideas from one central source, nor do they come at me in the same way. And I don't think I've ever expected I would for anything, not science, not singing, not writing, you name it. If I ever had to rely on one source for inspiration and motivation, yick. So I guess my advice to writers when faced with this question is to first ask, "Do you mean in general or for one story in particular?" Get the person asking to think about it a bit.