45 Exalted Reputations

While another title at 50 reputations would be welcome, I'd think they rather give out some other in-game rewards like a pet or a mount. Personally I'd vote for a trinket that summons 5 non-combat groupies following me around, basically doing stuff like fawning and swooning.

That'd make me feel even more exalted.

Edit: The 50 reputation achievement is now live on servers! The reward for this achievement is the title "the Exalted". The bad news is, people who have previously earned "the Exalted" title but fall short of 50 exalted reputations will have their titles removed. In my memory, there has been no such removal of achievement titles, except back in the time of Vanilla PVP.

Losing the title makes me a bit sad, as I have to go out of my way to find more factions to grind rep with. Cataclysm didn't add that many new factions.

Edit*2: The change has been reversed and people who earned their Exalted titles get to keep them.

Factions which you have had at Exalted but lost at some point no longer counts towards the achievement.

You get 10 Achievement Points for every step of 5 exalted factions after the "Somebody Likes Me" which gives you 10 points after getting one exalted faction.