Hi Rob! I'll start with I haven't lived in Seattle for a few years (but I'm coming back). When I was there my favorite shop was Sturtevants. Not terribly convenient from Seattle proper, but worth it in my opinion. You can also go to REI, although a friend of mine just had his board ruined when they left the wax iron on for too long, then tried to cover it up so he didn't notice until after a day of riding.
If you have kids who don't know how to ski yet, make 2 appointments for them at Mini Mountain in Bellevue (1st appt where you drop off your skis for tune up and the 2nd where you pick up your skis after tune up is complete). You get your skis tuned and your kid(s) get 2 great lessons! See my review of Mini Mountain here: freshchalk.com/Troy#7577