You might think combining the hyper-social Twitter with the (arguably) antisocial World of Warcraft would be a bad idea, but someone's gone and done it anyway.
TweetCraft is an add-on for World of Warcraft that will let you use Twitter from within the game. Once installed, it sits alongside your game and then uses a script to read and write tweets to the outside world. As per Blizzard's rules, y'see, add-ons aren't allowed to interact with the Internet.
Be careful too, because the default settings mean that the app will auto-tweet when you do all kinds of stuff - like changing zones or getting achievements. If you don't want it to do that, you'll need to poke around a bit in the config files.