I honestly think POTC 3 will be as successful as POTC 2 (its $400 million gross caught me completely by surprise), judging by the audience reaction. Which means POTC 3 will most likely be the highest-grossing movie of the year, but then again, it could be lower. (My estimated opening day gross for POTC 3 will be $60 million, and maybe a $450 million domestic gross by the time it's done.)
I really don't think why people are thinking Spider-Man 3 will emerge the ultimate box-office champ, when there is heavy competition after it. I think Spider-Man 3 will easily hold its own, although I don't think it'll reach $400 million like the first one did. I think it'll do Spider-Man 2 numbers, around $300-$375 million tops.
I'm not so sure about Harry Potter and the Order of the Phoenix -- I am positive that it'll make over $200 million, but considering the yo-yo-ing success of each film (HP 1 = $311 million, HP 2 = $260 million, HP 3 = $249 million, HP 4 = $290 million) I really can't pin down a specific number. But I guess that since HP 4 enticed more people, I guess the films' popularity is going back up and perhaps a $300 million gross, if it's lucky. (I will see the movie and hope the best, though.)
Since it's a Pixar movie, Ratatouille will bring in the dough as well, and also Dreamworks's Shrek 3. I'm not so sure about Ocean's 13, Evan Almighty, Transformers, Fantastic Four 2 and The Simpsons Movie.