Some Seattle Ground Transportation Options:

Seattle tour information and Pacific Northwest sightseeing tours
http://www.graylineofseattle.com

Gray Line Seattle Downtown Airporter
http://graylineseattle.com/airportexpress1.cfm

SEA-TAC Airport: Ground Transportation Rates
http://www.portseattle.org/seatac/ground/groundrates.shtml

SEA-TAC Airport: Shuttle Bus
http://www.portseattle.org/seatac/ground/shuttlebus.shtml

Seattle Metro Online (Trip Planner, Pass Sales, & Timetables)
http://transit.metrokc.gov