The Gap announced another 40% off sale for Facebook fans for Thursday 20th. The sale is only for one regularly priced item, not your entire purchase.
It doesn’t look like you need a coupon- just say THURS40 at the counter or you can get 45% off with your Gap card by saying THURS45.
You can get all the details on the Gap sale here.
This is not valid at outlets or factory stores.