I've just reread the book, and the parts I'm most interested in seeing are the scenes in Aslan's Country and Bism, I think. Maybe I have a thing for unusual landscapes.
I'm looking forward to seeing little things like Cair Paravel again - it'll be interesting to see how similar/different it is from LWW (and we've never really seen the inside, have we?) - and of course the freeing of Rillian and the final confrontation with the LotGK.

To name a few off the top of my head...

Meeting the aged Trumpkin

Meeting the Parliament of Owls.

Meeting Puddleglum.

Meeting She of the Green Kirtle, and her quiet companion.

Meeting the Giants of Harfang.

Dinner with an enchanted - and perhaps emotionally unstable, if you buy the BBC adaption - Black Knight.

The final showdown with the Lady, and Puddleglum's speech.

Caspian and Eustace beating up Jill's bullies at the end, and the Headmistress loosing her head and getting elected to Parliament. That was awesome.

Yeah... most of the things I look forward to is the meeting of characters. While these are the scenes I look forward to, they are also the scenes I fear will be altered. I'm also 99% that the Headmistress becoming an MP will not appear in the film, as amusing as it is to read, I'd be happy if they just keep the bullies being beaten up.

I'm looking forward to seeing Eustace and Jill in Cair Paravel the first night in Narnia having dinner and before they go to the owl's council. Cair Paravel's such an integral part of Narnia to me and there are so few scenes actually in it that I'd really like to see this

I'd like to see the opening where Eustace finds Jill and tries to convince her of his change and telling her about Narnia.
Definitely Jill and Aslan.
I'd like to see them capture Eustace's emotion at seeing Caspian.
Puddleglum's intro.
The strange trenches.
Meeting the two strangers
The dream
The journey into Underland (seeing all the sleeping creatures especially our first glimpse of Father Time.)
The meeting and rescuing of Rilian
The Lady's almost enchantment.
Bism.

EDIT:
Oh, and of course Caspian's retransformation and the bullies' lesson.

I think I am most looking forward to seeing more of RD. I don't know how those scenes will play out, but I'm excited. Seeing a reconstructed Cair Paravel and (who knows?) maybe the Dawn Treader, also rank pretty high. I also can't wait to see Harfang. Even though we know the secrets of how it's done, seeing giants and tiny people interacting is magical.