Angela Booth suggests that experienced writers can use journals as their idea banks:
If you’ve been writing for a few years, your journal acts as your idea bank. It’s best to maintain several journals: one for ideas, another for essays, as well as a journal for a long project like a book.
If you’re writing a novel, for example, your journal will keep you “in” the novel, even if you have to leave the project for a week or two.
An idea bank would be helpful for anyone who works with information and ideas. You don’t have to use a paper journal, because there are lots of desktop or online solutions too. You could use a wiki, a note-taking application, a desktop information manager like DevonThink or PersonalBrain, a password-protected blog (to keep your ideas under wraps while they’re gestating), or text files.
How do you capture your ideas?