ORCA card
This is the regional transit card. I bought this because I wanted to travel from Lakewood to Seattle. This is suppose to cover most of the buses, trains and even Ferry.
One Regional Card for All (ORCA)
The ORCA card is all you need to pay your fare on Sound Transit, Community Transit, Everett Transit, King County Metro, Kitsap Transit, Pierce Transit, Seattle Street Car, the King County Water Taxi, and Washington State Ferries.
website: orca card