My anal retentive way to figure out if a sale is indeed an actual bargain. I type the regular and sale prices for the stuff we buy regularly from the sale papers and from our receipts into an Excel spreadsheet and calculate the price per ounce/pound/gallon. I've been doing it since the beginning of January and have a pretty big selection of stuff. My next goal is to try and figure out how often items we buy regularly (especially stuff that doesn't have a shelf life, like cat litter or laundry powder) goes on sale and how fast we use it. That way when there's a huge sale (or a sale and I have a coupon for something) then I can stock up and not even have to buy anything until the next time it's on sale.
In case you were wondering (or hadn't figured it out by now) I'm a HUGE dork.