Seattle, WA The City of Seattle runs a useful real estate mapping GIS tool: Seattle GIS Tool
The tool allows you to see building outlines, addresses, parcels and also right click on a property to get permitting info and other public data. This GIS tool only covers Seattle real estate inside the city limits.
King County King County also has GIS mapping tools and they cover all of King County
On Wicklundre.com, homes for sale in Seattle, Bellevue and other King County areas (where the parcel number is provided) are directly linked to King County's GIS map and parcel data.