First from the Huffington Post, they have the exclusive on the time travel episode, episode 12, titled "As Time Goes By." In that episode, a man is transported into present day. Turns out that man is Henry Winchester, the paternal grandfather of Sam and Dean (and John's father). The role will be played by Gil McKinney, who is better known for his roles on ER and Friday Night Lights.
The entire article can be found here: http://www.huffingtonpost.com/2012/11/30/supernatural-gil-mckinney-season-8_n_2220732.html#slide=1785654
The other spoiler comes from EOnline, in the chat with Kristin. This isn't a very specific spoiler, but it involves Sam and his meeting with the previously dead Don. Remember, they're guessing about whether or not this is real.
Dina: Hearing a theory floating around that Sam's girlfriend Amelia isn't real on Supernatural. Got any scoop on that?
Our source close to the show tells us that a love triangle of sorts is coming up between Sam, Amelia and her not so dead ex-husband, so we're assuming she's pretty darn real. (Sorry, we guess?)