The 2015 Summer LEGO Sets are now available for sale at LEGO Shop at Home and Toys R Us America stores. Sets include City Deep Sea, City Space, Creator, Mixels, Chima and more! Toys R Us is advertising that the sets are available in-stores only, but they are up online as well. There are also some reports that Star Wars are available at Toys R Us stores as well.
Remember that until May 31st, 2015, LEGO Shop at Home (USA | Canada | UK) will be offering a free 30305 LEGO Marvel Super Heroes Spider-Man Super Jumper set with purchases of $50 or more (£25 for those living in the UK).
Thanks to forum members ncbarrett and Pumpkin Ecks for the tip!