"What's the title?" is the one of the first things a writer is asked after they've answered (or tried to, or avoided answering) "What's it about?". Titles are a book's introduction to the public. Tricky beasts.
Some authors have their titles from the beginning. Some have it jump out of them from their manuscript. Others have it thrust upon them by editors. I've never had the latter experience but the first two have happened. My games are titled from the beginning - simply because key words in the title help it to sell. "Death" is huge, as is "Murder". Clever titles do not sell murder mystery games. Clever titles can sell books, however. People wonder "What does that mean?" and pick up the book to look at the inside cover and you're half way home.
Titles can't be copyrighted, which is odd. Who is going to write "The Great Gatsby" (the story of a giant dog named Gatsby)? Imagine an author submitting a new manuscript to their editor entitled "Gone With The Wind" (story of a meteorologist) , or a screenwriter submitting "The Sound of Music" (about an orchestra). These are not likely scenarios. On the other hand "My New Book" is not apt to fly off the shelves either.
My book titles come from Shakespeare. Spy My Shadow is from "Richard III" and I like it because both the title and its source make sense on many, many levels. Keep the Key is from "Hamlet" and is one of the few things I know about that book, other than the presence of my detective and the setting. Keep the Key came early whereas Spy My Shadow came about half way through the writing process. I find the process very similar to the exercise of naming characters; when I get the right one I can almost hear a 'ding' in my head.
When do your titles present themselves? Is it an easy process or a difficult one? Do you use working titles ("This D#&@ed Thing") until you hit upon the correct one? Or do you just not care and leave the title selection up to someone else?