I'm not sure if it's been listed:
A.C. Moore (crafts and supplies store) offers discounts. It's on the eastern side of the US, a chain. It may only be in the northern part of this area. (You have to show them ID or a pay stub to get the discount.) Barnes and Noble used to offer a discount, but I'm not sure if they still do. (I saw it mentioned above.) As I also saw mentioned, some places will offer discounts to any non-profit; you only have to ask.
If you're a member of the National Educators Association (NEA) they have numerous discounts for members. In addition, Ann Taylor offers 15% off for teachers. Barnes and Nobles offers varying percentages off depending on time of year and promotion.
One good option is to ask! You'll be amazed how many places will help you out if you tell them you're a teacher or if they know it's for your classroom. I regularly ask local businesses for gift cards or promotional materials for my students. I'll use these as incentives for attendance or motivators at the end of a long quarter. It never hurts to ask, right?
Add Banana Republic and JCrew to the retail list (they have a 15% educator and student discount). This means Gap and Old Navy are probably also included.
All the local museums, science centers, and any other educational venue which requires membership or a purchased ticket in NC are free for teachers and homeschooling parents.
AT&T and Verizon offer discounts to state workers (so public school teachers are included). I'm sure other cell phone companies would comply if there was a threat to switch.
Many YMCA's offer educator discounts (but I believe this varies by ownership and location).
Most major bookstore chains have teacher discount cards or events on a regular basis. Barnes and Noble is one, specifically. Macy's has teacher night events where you can shop after hours for 20% off.
Target and Shopko have also been known to offer discounts on selected items for teachers.
It is interesting that stores offer a general discount for all teachers in the US. Here in Britain, the kind of discount that you can get depends on where you work, and normally you receive a discount in local stores in your area rather than nationwide. Therefore I get a discount on public transport in the county where I live, and also selected discounts in some stores.
Christopher Banks clothing store offers a teacher discount on clothing. I am not sure if it is a special event(s) or all of the time. I also receive a discount on my cell phone service because I am a teacher. I guess the lesson here is that it never to hurts to ask -- all they can say is no.
Staples and Office Depot stores in my area give discounts particularly at the beginning of each school year, with the idea being that teachers will be stocking up on the basics that will be needed throughout the coming year.
I have found many on-line companies which offer teachers discounts. My suggestion would simply to contact the customer service of any company which you are dealing with and ask them if they offer discounts to teachers. My favorite place to use my "teacher card" is my local movie rental store. I get free movies if they are used in the classroom.
There are quite a few places that have teacher discounts- you just have to be sure to ask at the checkout and bring proof that you are a teacher. New York and Company gives a 15% discount all year. Barnes and Noble has an educator program where you can get 20% off of items all year. Other places have designated "teacher appreciation" days; you have to keep your eye out for those.
This website has a list of various places that give discounts and have educator programs.
Big Lots is a chain that often rewards teachers with substantial discounts, sometimes including discounts on top of regular discounts. You may be able to find out more about this by visiting their web site: http://www.biglots.com/