Consignment stores are wonderful, I buy and sell at my local one all the time! Clothes are great, but then as they get older, toys and books too - it's so nice to get fun things for just a few dollars, then if your child tires of it you just resell and let them pick something new the next time you visit.
I don't live on the eastside, so I could only tell you all the ones near me (in Edmonds) and in the northend! But I'm sure there are some great ones near you, and other moms that live over there will know them. If you are over this way, I highly recommend A Children's Warehouse in Mukilteo (right on the Muk Speedway). They're prices are a bit on the high side, but they have a lot of European and boutique brand things that you might not find used elsewhere, and a wonderful selection of quality shoes. Also they get tons of Gymboree, and lots of complete sets that include socks and hair access. I could browse there for hours. Also up north, in Everett, Just for Kids is great, with lots and lots of stuff, and very low prices. It takes a bit more rummaging, and they generally don't keep things in sets, and the quality is not quite as nice, but for low prices they can't be beat!
Anyway, happy shopping - I love buying clothes for my kids, and consigment is the way to be able to do it the most!