Ten Ren Tea Co. in the I.D.(506 S King Street, just west of 6th Ave. S) has a fantastic selection of green, white and oolong tea, with a very unfussy presentation and the extra added bonus of sitting down to a tasting, if you have the time. (see past review)
Miro Tea in Ballard (5405 Ballard Ave N.W.) presents a stunning portrait of a modern tea parlor, with some pretty mean sandwiches. The interesting, rich wood detailing, inventive tea drinks, and a great location are enough to make a tea drinker out of anyone.
I still need to sneak in and try The Arctic Club Hotel's new afternoon tea service, served Wednesday through Sunday in the Polar Bar off the main lobby.