Most newspapers now have an online presence, and the majority have a search function allowing you to seek articles of interest in their archives. Unfortunately, most only have their recent archives - perhaps one to ten years - accessible online. Still, this is enough to help you find obituaries, mentions of possible relatives still living in the area from which your ancestors moved, photos of buildings and other places that factor into your genealogy, and other leads and clues.
And if you don't find what you're looking for, these sites generally provide contact information so you can call or e-mail for information about where to find older issues of the publication. Here are some sites that will help you tap into the wealth of information available through newspapers: