The wedding scene in which Mark gives Juliet and Peter the best wedding present ever - a performance of "All You Need Is Love" with full choir, orchestra, and guitars and drums.
Even more so when you later realise that he actually is in love with her himself...
Mark, Juliet, cue cards and fake carol singers, as Mark finally says what he has wanted to say to Juliet since he first met her. THAT is his CMoA.
Sam's wild run through the departures area of Heathrow Airport to catch Joanna before she boards her flight back to New York; after pulling all sorts of gymnastic manoeuvres (especially in the uncut version of the sequence) and benefitting from the gate staff being distracted by Billy Mack's video striptease, he finally catches up with her just before she walks down the jetway to the aircraft... and, better still, learns that she has been just as smitten by him as he has by her, and really was directing her performance of "All I Want for Christmas Is You" to him as a way of telling him this.
On a related note, Olivia Olson's performance of "All I Want For Christmas Is You." Even better when you learn she actually had to tone down her singing skills so people wouldn't assume she was dubbed.
David's driver pulling out his operatic singing voice for Christmas carols.
This movie helped kick start an entire genre of film (Ensemble cast in a rom-com). How awesome is that?
The Prime Minister's Rousing Speech, set to"PM's Love Theme". In which he verbally burns the US President, gives a massive shout-out to the great history of Britain, and serves notice that the UK isn't going to simply take what the US dishes out anymore. It was instantly beloved across Britain and became the centerpiece of a "look how awesome the UK is" advertising campaign.
It was also popular among liberal Americans, who would have loved nothing more than for Blair to do that to Bush (and knew perfectly well it would never happen).
Billy Mack's passion-less cover of a well-known song managed to outsell the latest boyband album.
Red Nose Day Actually
The fact that Sam happened to run into his childhood crush again in a city as massive as New York (they apparently had lost contact in the 13 years in between). And is together with her. And the fact that, in an inversion of usual gender roles, she asks his father for permission to marry.
. In which he verbally burns the US President, gives a massive shout-out to the great history of Britain, and serves notice that the UK isn't going to simply take what the US dishes out anymore. It was instantly beloved across Britain and became the centerpiece of a "look how awesome the UK is" advertising campaign."I love that word "relationship". Covers all matter of sins, doesn't it? I fear... that this has become a bad relationship; a relationship based on the President taking exactly what he wants and casually ignoring all those things that really matter to, erm... Britain. We may be a small country, but we're a great one, too. The country of Shakespeare, Churchill, the Beatles, Sean Connery, Harry Potter. David Beckham's right foot. David Beckham's left foot, come to that. And a friend who bullies us is no longer a friend. And since bullies only respond to strength, from now onward I will be prepared to be much stronger. And the President should be prepared for that."