I think Eclipse is my favorite book, although the first part of Breaking Dawn is close. There are so many scenes that they should put in the movie, but maybe there are some scenes that Melissa will write that are good too. These are my favorites and ones I think are necessary:
1.They have to tell Rose's story because it's essential to Breaking Dawn and the alliance she and Bella share. But then again...they should have told about Jasper's abilities in Twilight so that New Moon didn't have such a difficult time introducing it but they didn't...who knows. But I think that everyone, even the "haters", will appareciate her story and the revenge she took.
2. The werewolf punch scene. Bella asking Charlie for a crowbar and Edward telling Jacob that if he kisses her again without her consent he will break his jaw.
3. The bedroom scene after Edward has Alice kidnap Bella. And I loved the whole "Angry grizzly bears..." threat.
4. Jasper's story or at least the majority and how he came to Alice and they came to the Cullens.
5. The tent scene with Jacob and Edward talking. I soooo wanted the scene with Alice and Charlie in New Moon but they didn't do that...they just can't cut the tent scene.
The morning after, when Bella can't get out of the sleeping bag and Edward asks her "Did you want me to take him arms all the way off?"
6. The second bedroom scene where Edward actually proposes and shows her the ring. When Edward breaks the bed trying to prove his point about it being dangerous for their relationship to become more physical and then trying to explain himself because he's honestly old fashioned. Edward trying to cover up the fact that she's just made him the happiest person in existence when she agrees.
7. Alice begging Bella to let her do the wedding...and Bella asking her to be the Maid of Honor.
8. Edward and Bella talking after she leaves Jacob's house. Him telling her he's never seen her in such pain and wondering if asking her how he could possibly be the right choice when it hurts her so much.
9. The meadow scene with Bella trying to convince Edward that waiting until they are married was the right decision.
Well...they are out of order but you get the idea.
I know these won't all be in the movie...but a girl can dream. /sigh
Edit: Thought of a couple more:
10. Bella getting angry when Jacob tells her that he isn't aging: "Did you seriously just stamp your foot? I thought girls only did that on TV."
11. The scene where Jacob cuts his hand and Edward asks Bella why she stabbed him because they leave the bloody knife on the counter.
I'm sure there's more...I'll post if I think of them.
Edit: Thought of one more scene/line that needs to be in Eclipse.
The scene with Carlisle calling the Denali clan for help, and their refusal. At this point, they have not mentioned that Laurent went to stay with Tanya and her family and that he and Irina became close. Which is the whole reason behind Irina being angry with the Cullens and why she ultimately comes to see them in Breaking Dawn. That she sees Renesmee (what she believes is an immortal child) with one of the wolves makes her even angrier and is the reason she ends up going to the Volturi. Hope...hope...hope they put that in.