While not much of this is new, and seems to fall mostly in line with a few others like Harry or Hastings, there has been some misdirection of late on other sites, so I thought I would help solidify what I have heard and what I think.
This is a combination of my thoughts and whispers I have heard of late.
May : Necron 2nd wave
Jun : Chaos Space Marines or Dark Angels?
Jul : 6th edition.
Aug : Chaos Space marines/ Dark Angels?
Sep : 40k Starter set : Dark Angels v’s Chaos
Oct : 40k codex? Warriors of Chaos?
Nov : The Hobbit
Jan: Hobbit Box Set
Feb: Tau (this is what I have been hearing behind closed doors)
late 2013: Eldar
Notice how I did not place a large flyer release anywhere in the list. Although flyers seem to definitely be set for 6th edition, I have gathered that it will not be a single big release. Instead that it just might very well correlate with a Dark Angels codex and release in August. (In essence giving other space marine chapters their flyer as well), and then another small release in September.
With flyers we have heard that an Ork flyer was likely spotted, and a release set for later in the year makes sense.