The SPU databases that index newspapers and such are listed both here and (somewhat more selectively) below.
The online indices offered by the Seattle Public Library should be (unlike those offered by the University of Washington, below) accessible from anywhere via a Seattle Public Library account, for which everyone who studies or works at SPU is eligible. Here is a list of the SPL indices not offered by SPU:
Search for the titles of specific online newspapers offered by the Seattle Public Library here. Be aware, too, of the newspaper indices offered by the public library system from which you hail, whether here in Washington State (King County Library System, Sno-Isle Libraries, etc.) or elsewhere.
Some of the online indices available at the University of Washington may reach further back in time, or offer more in the way of full-text, than those available here; most must of course be consulted on site. Among those not offered by SPU (e.g. Newsbank Retrospective), or offered in enhanced versions (e.g. Newspaper Source Plus), are the following:
But see also (in addition to those at other universities) the UW's various Research Guides, for example
And don't forget to search for holdings of a particular newspaper or magazine in the UW catalog. Those of you doing research into the long pre-2001 history of the U.S. presence at Guantánamo may want to consult the University of Washington's retrospective newspaper and magazine indices as well.