We have an extensive collection of mostly Oregon newspapers on microfilm. See the inventory for a list.
Historic Oregon Newspapers online gives you access to a number of Oregon newspapers from their earliest dates through 1922. (However much more is available on microfilm.)
The Access World News database has the current and historical Oregonian, the Eugene Register-Guard from 2001-present, and current and historical Seattle Post-Intelligencer. It also covers more recent years of many local Oregon papers.
For national coverage, try the Historic LA Times and NY Times, and Nineteenth Century U.S. Newspapers: