Emoji Keyboard
Just arrived the scene, the Emoji keyboard!
this is a actual keyboard, from http://emojiworks.co/
Emoticon Keyboard Stickers
If you want emoticons, you can actually buy the stickers. See: emoji keyboard.
How to Input Emoji
On the Mac, you can set your keyboard to input emoticon. See: Mac: How to Create Keyboard Layout and Keybinding
For Microsoft Windows or Linux, you can just copy and paste. See: