Software For Writing

A colleague asked me for recommendations for software that could help writers organize their business writing. I know about the great software for writing screenplays, but if anyone has recommendations for software that helps you put ideas, quotations and other bits and pieces of work on "3 x 5 cards" (electronic ones that is) and has flexibility in letting you move ideas around and structure your essay or proposal or article or research paper, please let me know in comments below. Thanks.