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:
History Resources on microfilm. This page gives you a list of Oregon, Washington, and Western U.S. primary documents available on microfilm at the UO Libraries Microforms Dept. Some of these collections have a print reference guide to help you locate what you need. These may be located in KNIGHT Reference, and should be mentioned in this list.
See this page for other Subject Guides to microforms that may be of interest, including: Native American Studies, Presidential Papers, and Census and Newspapers (already mentioned on this page, above.)