The first two resources listed below are the best starting point for searching for US newspaper articles from the past 20 years. To check the availability of a specific newspaper, search its name in the Journals search.
With each of these newspapers, you have the option to search the last 25+ years of issues, or browse the latest digital editions in color PDF.
To browse, after opening the link, scroll down to the list of sources and click the one that says "Image" under the Format column. You'll see links for browsing the last five issues, or choosing an issue by date.