A list of April Fools pranks for 2011:

• Introducing Crabby: The Dungeon Helper
• Preview: Tomb of Immortal Darkness
• Hold the Power of the Horadrim in Your Hands
• A sneak peek of Patch 4.1.11, including:
  • Random Guild Finder
  • An Appearance tab for non-combat pets
  • Class changes (druids as vehicles!)
  • Reduction in fun for all items
  • ...and more!

Fansites

• MMO Champion has revealed details about new items available at the Blizzard store: Divine Wings and Wings of Chaos.
• MMO Champion has also dug a little in the game files and found not only some Pandaren masks for Hallow's End, but a possible video that hints at their inclusion in the game.
• Paragon has revealed new features of the Ragnaros raid encounter, Heroic Firelands.

• WarcraftPets.com informed us of a change to companions, our small non-combat pets: they're now getting a loyalty meter! Coming with Patch 4.1.

• Wowhead changed to Rifthead for the day, complete with an official announcement.