The absolute worst place to impulse buy is Costco. You can easily ring up $200 in items before you know what hit you. As much as I enjoy shopping at Costco, I can never get food items there. By the time I get near the end of say, a box of cookies, I have no desire to eat cookies for months. DVD’s and Video Tapes are another story entirely.
If you are scrambling around at the last minute online for shopping, I suggest you take a look at HappyCoupons.com. They are one of the sites that feature discount codes for all sorts of merchandise. If you are shopping for DVD’s, I recommend DVD Price Search. On the site you can compare prices of DVDs on various e-commerce sites as well as get some coupon codes.