Easter eggs have always struck me as weird. On one hand, the bunny keeps hiding them, so I guess he doesn't want you to find them. But then he makes them brilliantly colored, which blends in with nature not at all. So which is it, Easter bunny? Do you want us to find your eggs or not?
In a similar fashion, some MMO Easter eggs are cleverly hidden, undiscovered by most who run on by. Those eggs tend to reward the observant, the meticulous and the just plain lucky. Then there are the eggs that the developers all but shove in your face as if to say, "Hey! Look at this! It is wacky and out of place and breaks the fourth wall!" Those eggs are available to all, usually whether you want them or not.
So what are your favorite Easter eggs in MMOs? Are they oblique references to pop culture hidden in item description text? A remote area that's almost inaccessible unless you know the exact trick to getting there? A secret buried inside a quest that unveils itself if you know just where to look? What makes you gurgle with delight when discovered?