From 1997: Cuba Gooding Jr.'s speech. The orchestra tried to play him off the stage, but it only ended making his speech sound all the more epic. By the end the crowd was roaring with approval and many gave him a standing ovation.
From 2003: Adrien Brody not only winning Best Actor for ''ThePianist'' (becoming the youngest actor to do so, at age 29), but halting the playing of the wrap-up music, to the rapturous applause of the audience, and getting two standing ovations.[[
From 2014: Steve McQueen became the first black producer to win an Oscar for 12 Years a Slave which won for Best Picture. After giving his speech, he jumped with joy onstage while the cast and crew cheered.
Also, Lupita Nyong'o became one of the few actresses to win an Oscar for her film debut.
From that same year, Gravity completely destroying the Sci Fi Ghetto, winning 7 Oscars out of its 10 nominations, including a well deserved Best Director win for Alfonso Cuarón (who also won for Best Film Editing earlier that night).
From 2015: Polish director Pawel Pawlikowski, whose Ida won Best Foreign Language Film, refusing to cut his acceptance speech short and outlasting the inevitable "play-off" music.
John Legend and Common, having won Best Original Song for their Selma tune "Glory", making pointed reference to civil rights struggles past and present during their acceptance speeches. Made especially effective by the controversial scarcity of non-white Oscar nominees that year.
Graham Moore's acceptance speech after winning Best Adapted Screenplay for The Imitation Game. Full stop.
The Everything is awesome!!! performance.
Lady Gaga's phenomenal take on The Sound of Music doubled with an appearance by Julie Andrews to celebrate the 50th anniversary of the film.