Anyone seen a movie in which an actor does a riveting stage performance?!

Anyone seen a movie in which an actor does a riveting stage performance?

Alright,we all know that acting is art,which is based on creative,instinctive actions and reactions employed to convince or trick us on a self-embarked fantasy level or plain.People who can't handle horror movies are only too overly convinced mostly my means of extra pints of catsup or red sauce(although they know this is never real blood nonetheless).Anyway,have you had the pleasure of watching a movie in which an actor does a stage performance,be it song,dance,tap,that is over-the-top(at least to you)and is clearly the starring actor without a stand-in,voice-over,computer imposed(graphics)or other smoke&mirrors,that you thoroughly enjoyed?These are very rare treats that always impress and fascinate me when it happens.My favorite actor stage performance for a movie was Thandie Newton playing a Jazz Singer in"Gridlock'd"(1997)She did a supporting role in the film as a mostly strung-out junkie,but once she got on stage to perform a Jazz song,it was magic!Name your favorite and say why.

"How to lose a guy in 10 days "...funny movie, a short stage performance by Matthew McConaughey and Kate Hudson (somewhere in the end).

note: Matthew said that Kate had to pretend she couldn´t sing that well since he is such a bad singer ...xD but it is very funny and not that bad, I think.
I just like that he had this courage to sing even though he can´t. that makes him even a better actor than he already is :)