After you've completed your daily heroic/normal dungeon quest for the day, go to the questgiver in shat at the exact time your daily quest log resets (3am server). Right when it resets, talk to the questgiver and you can get the same daily from him again for the next day! Gotta be quick to make it before the dungeon changes.
This may also work for the daily BG and cooking quests that change too.