I get most of my supplies online at either:
I used to shop almost exclusively at discount school supply, but oriental trading co. has really been expanding their teacher materials sections. I also shop at Michael's and AC Moore when they put out their coupons. AC Moore has a coupon every week for 40% off one regular-priced item. I'll go, get my one item, and go home. Then I'll do it again next week, until I don't need anything else. Michael's has coupons every week, too. And they accept each others coupons, if only one of those stores is near you. And I'm always scouring Dollar Tree for good stuff!
In August, Staples, Office Max, Office Depot run sales on certain items each week. They usually limit it to 5 per person; so I take my family with me. I got Elmer's glue for 10 cents each, 24 count box Crayola crayons for 25 cents each, boxes of pencils and plastic pencil boxes for 10 cents each, and 12 count boxes of Crayola colored pencils for 25 cents each. I know it's too late for this year, but don't forget to check those ads next August! And go on the first day of the sale, before everything is gone. I missed the markers this year.
Becker's has a sale on everything in July (so you can get what you need for the next school year) if you are on their mailing list.
I also have a 15% code for Discount School Supply, good 'til Dec 31, 2007. I got it at my local naeyc convention: enter NJ15 as key code at checkout. (Free shipping over $79)
Oriental Trading Co. is always running free/reduced shipping deals. Check www.naughtycodes.com for current codes.