Once you really get the folding bug, having lots of paper readily on hand is essential. You'll find yourself saving the "good stuff" until you've tried creating that new model on the cheap paper first. You'll find that you need different kinds of paper for a special effect or gift. Here are some helpful paper sources that you may have overlooked.
1. Colored typing paper - At your local super office supply store (Staples, Office Max) you can inexpensively purchase a ream of typing paper in assorted colors. If the office supply store has a copy center in it, they most likely will be able to machine cut the paper for you for an extra dollar or two. If you have it cut large, you'll get 500 sheets of 8 1/2 inch square paper, or go for 5 1/2 inch square and get 1,000 square sheets from the ream. But be sure to carefully explain to the clerk that the sheets must be cut exactly square.
2. Memo paper - While your at the office supply store, you'll find inexpensive 3.4 inch (8.6 cm) square, 500 count, colorful assortments of memo paper, in nice plastic containers as well. If you haven't tried folding with small paper yet, give it a try. You'll be surprised at how cute the little rabbits and birds turn out. Litter the world with your little creations and leave people wondering where they're coming from.
3. Wrapping paper - To make really large origami models, wrapping paper can be perfect. Look for sturdy paper with color or print on one side and white on the back.
4. Scrap book paper - Now that scrapbooking is so popular, craft stores have aisles of paper in interesting textures and designs. Single sheets can be a little expensive but it's well worth it for the right origami model.
5. Decorate typing paper - Air brushing on plain white typing paper can give your models a unique appearance.
6. Dollar stores - For a good source of heavy duty wrapping/craft paper and scrapbooking paper, check out your local dollar store.
7. Folding bone - Good creases need a good edge. The flash from a gallon size milk jug's handle works in a pinch. And they're free. Look for them littering the floor of your grocer's milk case.
8. Origami clubs - There's power in numbers and clubs usually have enough members where they are able to buy origami paper in bulk at a substantial discount.
9. Use coupons - Craft stores like Michaels and AC Moore usually have 40% off coupons in the Sunday newspapers. If you can't buy in bulk, get in the habit of only buying origami paper when you have a coupon.