Some of my theories, SPOILERS!!!

[CrystalGazer]

Ok, Here are some of my theories.

1) Professor River Song and Donna could be the same person. I believe this because... How else could anyone know the Doctor's name?
I don't know if it was just me, but I freaked when she said he knew his name. I mean... the Doctor barely knows his own "real" name.
But Donna briefly knew everything the Doctor knows... She could have known his name.
And what if some of her memories started leaking back since the finale? Is that way Professor River Song keeps a Diary, just in case the Doctor needs to remove her memories again?
And perhaps... being part Time Lord (because the Doctor didn't take that away from her)... Donna lives longer. Which explains why River Song seems to be a future away from Donna.
Not to mention they look similar, Riversong just has curly hair and different makeup.

Eh, whovians? How's it?

2) The Doctor is going to bring Gallifrey back, possibly with Jenny. I forget which episode, but the Doctor said that "It wasn't time for Gallifrey to die." Usually, that means that the Doctor can possibly go back and save Gallifrey.
I had... more explination as to why I believe this could happen, maybe... Martha wanted to see Gallifrey, so did Jenny...

just for fun: Ms. Frizzle and her Magic School Bus- TIME LADY
Mary Poppins... TIME LADY  

[CrystalGazer]

C'mon! Someone critique my skills on Doctor-Who predicting.  

[Dante Alicheery]

That does make sense... better then the theory on Rose being River Song anyhow.

But I don't think they will bring back Gallifrey. It is my impression that the Time Lord's weren't stupid enough to have all of their people die when they knew that it was going to happen. Romana would have evacuated some of the planet or something so that the Time Lords would survive.

Perhaps they start a New Gallifrey?  

[Triska]

Or they might have pulled a really good stunt where they set the whole planet into the time vortex, and timed it so that it seemed to have been destroyed.

Donna can't remember. The Doctor said that if Donna were to remember just a tiny bit, she would die. And River Song never met or recognized Donna. And with a Time Lord's memory, it's not likely for her to forget.  

[Treesah Quiche]

I think that the Doctor is definitely not alone, and not just in the "Oh, hey, the Master's gonna come back and totally screw you over for a while" way (although I'm pretty convinced that that's going to happen again; the Master's too good of a bad guy to put to rest forever, and he's smart enough and ambitious enough to want to and find a way to cheat the death/limited regenerations thing).

How? Chameleon circuits/devices. To disguise Gallifreyan evacuees and hide them from the Daleks, their biological makeup was changed and they were scattered across time and space in their human[oid] disguises, without any previous memories of who they are/were, and a pocket watch that they keep around and don't notice.

But yes. Whatever's in store for the Doctor, I'm willing to bet the $3.76 I have to my name at the moment that Jenny's going to have at least a brief cameo.
 

[Triska]

I just re-read my post and realized that the last part wasn't clear. I was referring to Donna in the last sentence.  

[JackLantern2020]

I think it would be impossible for the doctor to know that all the timelords are gone. Also I think Donna will be back and as a time lady......kinda because in the whoniverse nothing is ever certain and she could go to rome and see a stone picture of her,the doctor and the tardis, it all come back and she regenerate. Thats my theory on that anyway.  

[Triska]

There is a complication on her condition. And it wouldn't be Rome. It would be Pompeii. If she were to regenerate, it would only be the one time I would think. It was like as if the Doctor past enough where one would be in there.

I'm wanting to see Jenny come back.  

[Aya Fox]

On the River Song bit, some one suggested to me that the only way the Doctor would give out his real name is that if he was married to them. The other bit on that, Rose couldn't be River, she's known as the Bad Wolf.

As others have said, Donna dies if she's remembers anything of her time with the Doctor. While she might also be the Doctor-Donna, she only had the Doctor's brains, she was still human. I don't think she'll regenerate.

Jenny's bound to come back at some point... [I was hoping to see her in the end with everyone else.]
Bringing back Gallifrey...? Sure, it would be grand to see the original Gallifrey before it was destroyed, the Doctor has been refusing to go back into time and go there... I think he uses the "crossing into established events" there so that he doesn't go back and change everything. Though, I will say it would be a tempting thought since that one Dalek [was it Kon?] did cross back into the Time War, but you saw what happened to him... Probably if anything, as Lupine Eyes already suggested, create a new Gallifrey.