You get 30% your entire order with the code 0901 and then an additional 30% off the highest priced item in the order with the code 8964. You have to enter them in that order. (I found out about this from Slickdeals.)
H&M has some things on their website that can be difficult to find in stores, like beauty products and home decorating shit. The downside is that you can't return anything you buy online to a store, so you have to pay for return shipping. Also, they don't have reviews, so it's kind of a crapshoot. But if there's something you know you want, now is a good time.