In suburban Maryland, Giant (and probably Safeway) double coupons up to $.50 (to $1). Superfresh doubles coupons with up to a $1.00 initial value, but I've never tried it there and the sign says "see store for details". There are a few Weis supermarkets in the outer suburbs, like Laurel, where they double up to $.55. The problem is finding a good enough sale.

A couple of weeks ago, Weis had 18 oz Corn Flakes for 2/$3, with no limit. I was able to use some barely expired $1.50 off 3 boxes coupons and $1.25 off 2 coupons to get 13 boxes for $1 and $.875 each. I have many more of the expired coupons (they were from one of those in-store coupon machines at Giant a couple of months ago). However, I didn't get a chance to get back to Weis and I didn't want to over-do it with the expired coupons. In case anyone is wondering, the scanner didn't accept the expired coupons, but the checker proceeded to enter the discount by hand without examining them closely. I know this was a bit unethical, but it's hard to get too worked up about coupon abuse.