Who needs more emails?
I know 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. Keep in mind that for many of these promotions, you must enter a special code when booking. If you don't, you'll likely be charged full price.