The best place to find coupons is still the Sunday paper. I don't get the Sunday paper but I know people who do and since they don't use coupons they give me theirs. Even if you have to buy the paper though, I think it is still worth it. Just a few coupons will save you the cost of the paper.
Important: If you are just going to buy it weekly from a store don't bother buying it on a holidays. There are usually no coupons on holiday weekends. When in doubt check the coupon schedule link in the right sidebar.
If you want the paper delivered, I suggest signing up for the "weekender" deal where you only get the paper on the weekend. Why pay for it all week if you won't be reading it?! If you want really great coupons, consider buying the Milwaukee Sentinel (or ordering coupon inserts online) to get better coupons than the GBPG offers. Coupons are regional and larger markets get better coupons. I should mention that the big city papers include coupons but not store ads so if you want to look at the ads you will still need to get a GBPG.
Which brings me to my next point... more than one paper is a good thing! Try to get as many coupons as you can. To stock up on the best deals you'll need more than one set of coupon inserts. Ask your family and friends who don't use coupons to save theirs for you.
There are also TONS of coupons available online (see links in the coupons tab above). Get cheap paper from a deal when you can or from Wal-mart (about $3/ream) to print your coupons out. Sometimes a coupon prints at the top of a page with an ad below. If you hit cancel right after you see the coupon on the paper it will save you the ink of printing the whole ad. If possible, I print the coupon, rotate the page, and use the "other end" of the page to print the next coupon. I really like the coupon sites like SmartSource that let you print more than one per page. I hate wasting all that paper and ink.
Company Sites and Newsletters
Love Betty Crocker or Huggies or any major name brand? Sign up for their online product newsletter and you may find printable coupons in your inbox. Get on their snail mail list too while you're at it! Don't buy a name brand product with out at least checking for a coupon. CouponMom has a searchable list of coupons that were available in past Sunday papers. Most sites limit the number of coupons you can print (usually 2) but occasionally coupons are "reset" or more than one site will offer some of the same coupons so you can print more.
Also remember "sqeaky wheel get the grease". If you get a defective product or are not satisfied with something you buy call (or email) the company and tell them. They will usually send you a coupon for a free item and often even more. Even if you call and just ask a question sometimes you will get coupons as well.
ALL YOU Magazine
Several women's magazines have an occasional coupon or two on their pages. Keep an eye out if you subscribe to any. The best magazine hands down for coupons, though, is ALL YOU. This magazine has as many coupons as a newspaper insert and will pretty much pay for itself when you subscribe. It is sold at Wal-mart if you want to check out a few issues before subscribing or just buy it there.
Word of Mouth Programs and Freebies
Sign up for "word of mouth" programs and freebies when you can. You will find your mailbox full of coupons, often high value coupons come in the mail directly from sources like this.
Keep an eye out... coupons can be found just about everywhere! Peelies are coupons that are stuck on a product and meant to be peeled off and used right away. Look for those red blinkie boxes at the store, they often have those right next to products that are already on sale! There are often coupons in or on product packaging. Coupons print with your receipts at some stores, usually for brands similar to the products you bought. Sometimes a friendly couponer will leave coupons on the shelf next to a product. Once you are looking, you'll find coupons everywhere!
Here is a list of helpful Coupon Terms and Abbreviations.