Admit it: You still get a little thrill of excitement whenever you run across a rare mob. There's always that thought that this -- this -- is going to be the time you kill something with a silver dragon around its portrait and something fantastically rare drops. Maybe it'll be a world drop like the Lei of Lilies. Maybe it'll be one of the game's first epics, a Staff of Jordan. Maybe you'll go out of your way to kill something and find a plate Of the Boar shoulder on it, and you'll wonder why you bothered in the first place. But hunting rares is, as they say, the triumph of hope over experience.
There are four achievements in the game concerned with hunting rare mobs, and they'll keep you running around Outland and Northrend for a while.
These achievements might get a lot harder when Mists of Pandaria hits due to cross-realm zones. They're not exactly easy to do right now, but they certainly won't get easier if you have to compete against a raft of off-server players. While we're not 100% certain that that's how things will function, right now I would classify these as achievements to do sooner rather than later. The only reason they weren't listed in that column is because I didn't think of them, but a few canny readers made the Cross-Realm Zones + Rare Mobs = Oh Shiznit connection.