I must get at least 2 20% off coupons every month in my snail mail. Did you know that if you order online and then take your receipt and 20% off coupon to the B&M store, they'll credit you the difference? It's good to know if your local store is out of the item you want but it's available online.
They also take their own expired coupons (just used a couple last week) and will take a competitor's unexpired coupons (like Linens 'n Things).
As far as online codes are concerned, I don't know of any.