I'm doing the old waiting game right now with my latest novel, the one set in Civil War Missouri I've been talking about the past few months. I sent a query letter to an agent and got a request for a partial and an outline, so I duly sent those off. Now it's Thanksgiving, then it will be Christmas. I have some waiting to do.
In the meantime, I'm still polishing the thing, and thinking about the two other books in the series. The book was originally going to be a novella, but then last year I realized I had enough material for a novel. I wrote it as a stand-alone book, making it less of a risk for publishers (always a good selling point) but I really want to make it a trilogy. There's a lot more to tell about the characters and the situation.
The trilogy is a well-worn format in speculative fiction, but I think it's a good one. You get a beginning, middle, and end, just as each individual book gets a beginning, middle, and end.
It's funny how some story lines bloom into entire series while others remain novellas or short stories. I'm not quite sure what unconscious creative processes are responsible for that, I just hope I get a chance to see the thing in print!