To have a truly stellar break-up scene consider the following:
(BU=Breaker-upper HB=the heart broken person)
1) Who is breaking up with whom? What is the BU's motivations?
2) How does the BU feel about the person he/she is breaking up with?
3) What does the break-up initiator feel about herself in relation to the break-up? (Does she hate herself for it? Does she dream of it?)
4) How does the BU show his/her emotions? (Is he/she normally a loud or quiet person? Touchy feely or not so much?)
5) How does the HB feel about the BU?
6) How does the HB show emotion?
7) How long have the two been together and what is there relationship status?
8) Is this a surprise for the HB? Maybe it's a surprise for the BU and he/she just snaps?
9) What things need to be brought up in this discussion and in what order? (Does it start with toe nail clippings, rise to tardiness, and end in "GOD DAMNIT YOU BASTARD, I KNOW YOU'RE CHEATING ON ME!" Or is it as simple as "I can't do this." "What?" "We're done.")
10) What do the characters need to feel and do once the scene is over?
And now for the examples (in no particular order)
1) Dangerous Liaisons. Never scene the movie, but I found the scene and it's AWESOME.
2) Grey's Anatomy: Addison + Derek (sorry for the music in the background, but a really excellent example if you watch the whole thing through)
3) Closer: Alex + Dan Breakup Scene
4) Tipping the Velvet: Nan and Kitty (You should skip till 1min and can watch till about 4:50. It's a great example of the before and after break-up)
5)Grey's Anatomy: Alex Karev + Izzie Stevens