I bought an awesome coupon organizer off of e-bay. It is a box, but covered in a stylish fabric, it locks shut, and when it is shut, you can turn it upside down or throw it around and no coupons will be out of place. That is important to me because I have kids, and I don't want them to accidentally spill it. It fits in the child seat of the grocery baskets. Mine has four sections, with about 15 index card dividers in each section. I can't post a link, but the seller was best-bargainz. It was a little pricey ($30 with shipping), but I think it was worth it. I am too self-conscious to carry a binder, but since this looks like a purse, I don't mind taking it in the stores. I buy 5 papers a week, and cut most coupons, and it holds them all just fine. Filing and pulling expired is so easy and quick. The only modifications that I made was to add tabs to the dividers so that I can easily see my dividers and I also made up my own filing system.
I don't post a lot, but I love this organizer so much I thought I would add my 2 cents! Thanks to all of you who share your tips!