Where do ideas come from?

Another question about writing I am asked is "How do you get ideas?" The simple answer is several ways.
1) Sometimes the story plays like a film. I need to write as fast as the film plays on those days. Those are the days that I buy legal pads at Office Max or spend hours at the computer writing down the story. These days are fun and fascinating. In fact, the characters take over, the dialogue is surprising, and the story goes in a different direction than I ever imagined.
2) Other days, the ideas are all mine. I wake up with an idea and flesh it out to see where it goes! Those days writing is fun but more like work.
3) Then there are the days when the ideas are half-baked, rare, and hard to find. Those days I may find an idea in the newspaper, on the Internet, or a magazine. I enjoy people watching and am cursed with teacher-hearing (hearing every conversation in the room!). My daily Bible study may also generate writing ideas for Bible studies.
Regardless of where an idea originates, writing is a guilty pleasure and yet still resembles work. My biggest challenge is to make me sit down and write.