I too gave up on the Sunday paper. Couponmom.com is a great site if you have the time and level of organization to invest.
I also like coupons.com.
I have two grocery stores I shop at and they both offer coupons on their site. If I load coupons to my store card they will NOT be doubled so have to be careful which ones I load and which ones I print. One store I shop at you can register your store card and you get special sale prices on different items each week - like half price Dannon yogurt, $0.57 for dozen eggs, BOGO cereal etc.
Target - you can print store coupons from their site which can be used in conjunction with a manufacturer coupon. This comes in really handy with diapers - $2 manufacturer coupon + $2 Target coupon = $4 off diapers. Their site will only let you print 2 of any one coupon so if they have a really good one I will call a friend to have them print 2 for me.
RedPlum and SmartSource (coupon flyers in the paper) have free sites you can print from. They are hit or miss for me.
I've used printed coupons for years and never had a store refuse one. I just recently got my mother started on using the sites too.
Good luck !