The Seattle area currently has a good mass transit system.

Seattle is located in King County. King County Metro is a county-owned public transit system consisting almost entirely of buses. The only exception is the new South Lake Union Streetcar. There was also a Waterfront Streetcar, but that line has temporarily been replaced by a bus pending contruction of a new maintenance barn.

Metro uses a very good mix of various types of buses providing both local and express service throughout King County. A bus tunnel under Downtown Seattle is used by many of the buses, providing faster trips through the downtown core and reducing the number of buses on surface streets. When the light rail line begins operations in 2009 the tunnel will be used by both light rail trains and buses.
More about Metro Transit My opinions about Metro Transit

The next county south of King County, Pierce County, also has a county-owned bus system called Pierce Transit. It provides service within Pierce County, including its largest city, Tacoma.

The county immediately north of King County, Snohomish County, has a public bus system called Community Transit.

The largest city in Snohomish County, Everett, has its own bus system, Everett Transit.

In addition to the county and city systems, there is a regional transit authority known as Sound Transit. Sound Transit operates a number of express bus routes and commuter rail service between Seattle, Tacoma, and Everett. They also operate a short light rail line in Tacoma and construction is underway on a longer light rail line from Downtown Seattle to Sea-Tac Airport, a few miles south of Seattle. The line from Downtown Seattle to Tukwila is scheduled to open 3 July 2009 and the final segment to the airport is scheduled to open in December.

Sound Transit is now starting work to extend the light rail line north from Downtown Seattle to the University of Washington. A proposal approved by voters in November 2008 authorizes Sound Transit to extend light rail from the University of washington northward to Lynnwood, to the south from Sea-Tac Airport to Federal Way, and east across Lake Washington to Bellevue and Redmond.