In Gap stores, bring in an old pair of jeans to "trade-in" and get 30% off of Gap's new 1969 jeans. Make that 35% off if you pay with a Gap, Old Navy, or Banana Republic credit card. Offer ends Oct 20. See the text of the offer here: http://www.gap.com/customerService/info.do?cid=55776
Of note, the strict text of the offer seems to indicate that as long as you bring in ONE pair of old jeans, you could get the discount on as many new pairs as you like.
Also of note, if you pay with one of those credit cards on a Tuesday, Gap will always take 10% off your order. From the text it doesn't seem like these offers are supposed to be combined, but YMMV.