UPDATE: For Android 6 (Marsh Mallow) use these steps
Google Keyboard is the default keyboard in the Nexus 5. By default, its configured to enable vibration on key press. If you are someone who dislikes this feature, here is a simple way of disabling it:
- Go to Home -> Settings -> Language and Keyboard
- Locate “Google Keyboard” and press the settings button next to it.
- Uncheck the tick next to “Vibrate on keypress”