The 2009 Oscars would not have been nearly as awesome without Hugh's phenomenal opening number. Incidentally, Anne Hathaway's performance alongside him (briefly) was so well received that she later went on to host the Oscars as well.
Hugh Jackman was genuinely naked when he filmed one of the scenes in X2: X-Men United so the crew decided to play a little prank on him. He ran down the hall and turned a corner only to find the entire female cast present to make catcalls and moon over his naked body while they waved money at him.
In his Inside the Actors Studio interview, he shares a story of auditioning for the role of Curly in Oklahoma! He goes to sing the character's opening song "Oh What a Beautiful Morning"...and forgets the words. "And there's only three bloody lines in the whole song!"