I use Moneysavingmom.conm, printablecouponsanddeals.com, coupons.com, and hip2save.com. I end up saving a lot with using coupons. Saved about 75% off my trip to Walmart last week. Ended up getting 4 jars of Vlassic relish free, got 4 of the 6 packs of frozen Milky Ways, Twix and Snicker Bars for $.97 each, got 2 boxes of Lance Crackerfuls for free. The couple that was behind me in line were so impressed they asked me where I got the coupons from!
I use southernsavers.com (this is probably most useful if you live in the southeast part of the US) and thekrazycouponlady.com. Both have been really helpful for me!