I'm a gamer!
Mechanical keyboards are the best choice for gamers for a number of reasons. First of all, they are durable enough to survive fast, hard and consistent key presses. Second of all, they give you a special feel and have a make a sound when you touch a key, so you will always know for sure whether you've pressed a key properly or not.
Programmable keys make for a better gaming experience, because you can set up shortcuts and key combinations to make your actions faster and more efficient in-game.
Another fun (though not necessarily crucial) feature is to get a keyboard with customizable back lights, so that they flash different colours - this looks really cool in a dark gaming room.
Note for gamers: Never buy a wireless keyboard, as it is less responsive and takes more time to register your keystrokes. They extra miliseconds it takes for a Bluetooth signal to reach your computer will definitely not work for you.