These stores double up to $1.00 DAILY:
Fry's
Bashas
Safeway
Occasionally they will triple up to $1.00 or double up to $2.00. Fry's and Bashas rain checks have a 30 day expiration date. Safeway rain checks are good for 90 days.
Doubling example:
.25= .50
.45= .90
.60= 1.00
.75= 1.00

Albertson's accepts competitor coupons; most will let you "stack" a comp cpn with a mnf cpn, although there are a few cases where an unknowing cashier won't allow it. Albertsons rain checks have no expiration date.

Frys, Bashas and Safeway have a policy of 3 LIKE COUPONS per transaction, although some cashiers let more through.

These four grocery stores do accept internet printed coupons (except if it's a coupon for a FREE product), unless a specific store mgr has refused them for his store.

Walmart of course price-matches and accepts mfg coupons.