Yes, it's more inbox clutter, but if you subscribe to the e-newsletters of the airlines, hotels and car-rental companies you like to use, you'll often find out before the general public about promotions like last-minute hotel discounts, weekend rental specials and flights that can suddenly be booked for fewer frequent-flyer miles. The prime deals are always snapped up quickly, so any edge helps. Note that for many of these promotions, you must enter a special code when booking — and if you don't, you'll be charged full price.