The Thrift Center in Renton is by far my favorite Thrift Shop in the area. Since it's a local store, they have a huge assortment of items for sale and at awesome prices. They have many different sale days including 30% off everything on Wednesdays and Saturdays. You will also find 50% and 75% specific colored tags every day. This is a great place for higher-quality clothing and items than the other thrift shops in the area.
You will find the store to be a little dirty and unorganized, but it's completely worth the savings. The racks near the cashier's are filled with both brand new and brand name items for cheap, so be sure to check those racks out.
They also have a ton of books and a better selection than I've seen in the other thrift shops.
The door to come in is hard to open and has been for quite some time, so remember to push a little harder on it than you would on a normal door. And don't expect to find a shopping cart here. They have two or three maybe and I've never been able to snatch one. Bring your stroller in if you have a baby.