Entertainment Weekly is featuring Supernatural's 300th episode with a cover article! It contains spoilers for episode 300.
Supernatural stars cover EW to celebrate 300 episodes (and an epic reunion)
More below the cut.
Update 9! 
Supernatural star Samantha Smith previews Mary's 'romantic' reunion with John
Supernatural stars Jared Padalecki, Jensen Ackles on why episode 300 isn't the show's end
UPDATE 8! Supernatural bosses on why now's the right time for John's return
UPDATE 5! More from the shoot
The cast explains the Easter Eggs in the shoot.
How 'EW' got that epic 'Supernatural' cover: Go behind the scenes with the Winchester (extended) family
Jeffrey Dean Morgan defends Supernatural dad: He 'shows love in different ways'
Misha Collins explains what Castiel's up to in Supernatural episode 300
During the Cover Shoot, the cast gave their thoughts about their family reunion and reaching the 300th milestone!

Entertainment Weekly also released exclusive shots of the emotional Winchester Reunion:

300 EW Winchesters

300 EW John Boys

300 EW John Mary

300 EW Cas Zach

UPDATE 2:  EW published smoldering hot portraits of our heroes later in the day!  Phew!

UPDATE 3: The emotional reunion of Jeffrey Dean Morgan and his Supernatural family
UPDATE 4: Tweets from EW
Here's where you can get the covers


 Hit 'Next' for reactions and tweets from the Jared, Jensen, Misha, Jeff, Samantha and Supernatural's Cast/Crew/Family!

 Check out the articles for spoilers and previews of the covers! Then come back here to discuss in the comments or in the discussion thread for episode 13.