Buy One, Get One 50% Off at Toys R Us
Valid Sunday 7/24 through Saturday 7/30, Toys R Us is running a Buy One, Get One 50% Off promotion for all* LEGO construction sets. Star Wars, Harry Potter, and Ninjago sets are excluded, however. As always, try and buy similarly priced sets and look for those sets with little if any extra TRU markup in order to maximize your savings. Lastly, you receive free shipping on orders that exceed $75. The sale went live at midnight and there are many nice sets in stock such as the new Red Cargo Train, Emerald Night, Medieval Market, Queen Anne's Revenge, and the Imperial Flagship.
Update: In some stores, the promotion is actually BOGO 40% Off.
Update 2: Star Wars sets are now also BOGO50% Monday 7/25/11 Only. The catch is that they only pair with non-Star Wars sets. The plus is that you can buy mulitples of the same set.