alright, I'm up to date on the manga and read the chapters as soon as they are released in english, so I already know about Madara's plan and stuff. But I was watching the anime subbed and just saw episode 138 which shows the end of Itachi and Sasuke's fight (where Itachi dies) and I noticed something that I had forgotten about... Zetsu said Itachi was "acting weird" and "not able to counter attacks he should have been able to counter easily". Zetsu then came to the conclusion that Itachi had been seriously injured before the battle with Sasuke.

I think Itachi tried to defeat Madara before trying to fight Sasuke... perhaps Itachi realized Madara wanted to use Sasuke for a part of his plan and that is why he attacked Madara. Afterwards, Itachi decided to use the last of his strength to remove Orochimaru from Sasuke and give Sasuke his Amaterasu hoping it would be enough to keep Madara away from Sasuke.

What do you guys think? I mean, who else besides Madara is strong enough to seriously injure Itachi?...