Granted the end of Winter's Heart clearly shows Demandred not to be Taim based on his ignorance of the Asha'man, but I found one earlier piece of evidence and I have not seen it posted yet. So here goes....
On page 441 of Winter's Heart (Out of Thin Air) Raefar Kisman tells us Taim AND Demandred told them to kill Rand. This would indicate that they are two seperate people. I have not seen this posted before, is it too obvious?
The only hang up is that Kisman goes on to say Demandred told them: "It would be better they died themselves then be discovered again. By anyone, even the M'Hael, as if he did not know of Taim's order." If Demandred somehow managed to dispose of Taim and take his place, etc, etc. (Which seems unlikely to me.) Why would give an order disguised as Taim and then again as himself? That does not seem logical to me. I think once and for all, the Taimandred followers have been defeated. Unless they are going to argue that Taim IS Demandred, he just doesn't want the other bad guys to know that he is......Give it up!!
Pento McGreno says: Goody, goody. OK, it's been well and truly proved that Taim isn't Demandred. Next, please.
just for the record I am not and have never been a supporter of the taimandred theory but this isnt evidence against it 
Green Gaidin,Ash'aman, he's your neighborhood badass man!
True Power is knowing that you can, but you don't. 
-Deathbone1 
Still a Stubborn supporter of Taimandred after KoD!
Be who you are
and say what you feel
those who mind don't matter 
and those who matter don't mind
Taimandred Followers Undeniably Defeated. Thank the Light!