Although they have an official release date of January 2013, the new Teenage Mutant Ninja Turtles LEGO sets have been spotted by numerous people on store shelves. Most reports seem to be finding the sets at Toys R Us stores, as well as (of all places) Walgreens. However, it should be noted that both stores are selling the sets for higher than the MSRP. If you're patient, you can probably get a better deal if you wait for the sets to appear in Walmart or Target.
Thanks to Shawn B. for sending in these pics from his local Toys R Us!