Just noticed today that many people doesn't know this when someone complained in trade chat about how he want Mekgineer's Chopper and wish there's more daily quest for him because he need reputation to buy the Schematic, and then many people start to agree with him.
You can get Alliance Vanguard/Horde Expedition by killing a mob in level 80 dungeon without wearing a tabard.
When I told them this they say something like "I've been wearing reputation tabards all the time because I don't want any reputation gain to go waste"
After I know that there're still many people who don't know this, I decided to share it here.
If this is in wrong section, please move it, can't think of other section.