If you haven't watched the movie yet it's probably better to avoid the many spoils contained in these videos.
How 'Guardians of the Galaxy' should have ended:
Guardians of the Galaxy dance-off gag reel clip:
Groot saying "I Am Groot" in 15 different languages:
Vin Diesel says 'I Am Groot' in 15 different languages on Jimmy Fallon:
Friends of the Galaxy: a mashup of 'Guardians of the Galaxy' and 'Friends':