On Origin, you can buy select Sims 3 titles and get one free (Offer ends September 13, 2012 at 10 AM PDT). The list is as follows:
Buy:
Sims 3 (29.99)
Sims 3: Supernatural Standard Edition (39.99)
Sims 3: Deluxe (49.99)
Sims 3: Diesel Stuff (19.99)
Sims 3: Generations (39.99)
Sims 3: Late Night...