3 for 2 at Boots in the UK
Boots has a 3-for-2 offer on LEGO and a wide range of other things on at the moment. There's quite an assortment of sets available so if you've been waiting for Star Wars or Indy sets to be available at a decent price, now's the time to buy either online or in your local branch although you're unlikely to find the large sets in it.
Many shops have 3-for-2 offers on at this time of the year in the UK, to encourage people to do their Christmas shopping early, so keep an eye out at Toys R Us and Argos in the coming weeks.
Thanks to Stuart for the info.
Update 22nd Sept: In the USA, you can find a 3 for 2 sale at Toys R Us. The sale will be until 26th Sept., but it excludes Star Wars sets. I've checked a couple stores in my area and found the sale there too, so you should have luck either online or at a store location. Thanks to "andy0002" for the heads-up! -jkool