Although it's not a hard achievement to get now that Blizzard have added city faction tabards, I'm still proud to say that I got Ambassador of the Alliance mid-heroic last night and the title 'Ambassador'. There was no sudden urge to spoil anyone with Ferrero Rocher, much to my tank's dismay :D
Lately I've been working my way through the new city tabards while we run heroics. I seriously recommend you do the same for any city factions you haven't hit exalted with yet, especially if you only need to get from revered to exalted. Collect the tabards you need from the city quartermasters located next to/near the flight points. They also sell cloaks which incorporate the city colours and coat of arms - these look great as part of a non-combat/RP outfit.
It goes without saying that you should always have a tabard equipped if you're running dungeons as you level!
As an added bonus for those efficient achievement hunters, each reputation will count towards achievements like 25 Exalted Reputations (my next milestone) or maybe 50 Exalted Reputations (a lot of respect to anyone who's aiming for that one).