Three things off the bat -
In the books, A is two people (Well, three, but I'm not counting Twisted). In the first four books, it's Mona. In books four through eight, it's Alison.
In the eighth book, it's revealed that Alison had a twin named Courtney. The four girls were actually friends with Courtney, who took Alison's place while Alison was shipped off to a mental hospital. Their parents had no idea. Then Alison came back and killed Courtney. She tried to kill the four girls, but she *apparently* perished in a fire, though that is yet to be determined.
And in the books, Spencer discovers that her dad cheated on her mom with Alison's mom. Alison and Courtney were her sisters (this is more plausible in the books because they actually look alike in the books, though who knows with the tv show).
Taking these things into consideration, it makes me wonder some things about the show, other than the obvious who-killed-Ali and who-is-A mystery. It's clear that it's straying from the books, since Jenna and Toby are still alive (in the books, Toby kills himself and Alison kills Jenna because she knew about the twin thing). But, like, the stuff with the shrink.
First of all, I think A would have to be someone who was terrorized by the girls, especially Alison. My theories are: Mona, Lucas, or Alison (her possible twin). Even Toby is plausible, though I want him to be/stay good. Then again, maybe Noel is involved. There are 92832908293 theories about that, like it's Maya or Ezra, but what would be the point of those two being A other than they can?
The show might be heading toward the twin thing, because of two reasons. One, when Alison was "in a dream" in the hospital (there was something like that in the books, and it ended up being real), and last night, when she appeared to Emily. In the last book, the real Alison (not Courtney, lol sorry if it's confusing), kinda hooked up with Emily and gave her hope, kind of like she did in last night's episode. Though Emily thought she was dreaming in last night's episode. What if she wasn't?
What if A's texts to the girls had a double meaning? A kept calling the shrink "she" - what if A actually meant Alison? "She's still alive" "She's running out of air" - they could have been about two different people or two at the same time. A would totally mindfuck us with that, don't you think?
Other things, I think that the Spencer's dad thing is going to happen on the show too, considering his conversation with Jason last night.
Also, on a shallow note (lol this whole show is shallow, but whatever~), YOU SUCK, WRITERS. WHY WOULD YOU BREAK UP SPENCER AND TOBY? I know Spencer wants to keep Toby safe but they better get back together, ugh. They're perfect. Also, I LOVE Caleb. What he said to Kate was hilarious. I wouldn't find it hilarious under any other circumstance, but Kate is a huge bitch and deserved it.
And a year and a half later everything will be revealed and I'll be 100% wrong, just you watch.