@HopeImNotCopywriting That's a very tough question. Even I'm not always sure where my inspiration comes from, but I think that's a good thing (usually, that at least means I'm not copying someone else's idea!).
A couple parts of my stories (and one short story that I'll be posting on New Years Day) came directly from dreams that I had. Those are the most fun to write, I think.
Deadly Angels and The Cloud Project were ideas that I bounced around for years, having long forgotten the sources of their initial concepts. It's like rolling a snowball: you can't go back and look at what's in the middle, but you get a cool, giant final product.
Then there are weird bits of inspiration. For example, Through the Hotel Door is an adaptation of a dream that my stepdad told me he had (he gave me permission to write it). And the idea for the Human Hunters (antagonists) in Deadly Angels was offered by a friend of mine, @cleo333, who first used them in her short story, "Perfect?". So I guess that's technically fanfiction!
I hope that answers your question, at least in part. :)