Aaaah the good old days of the Xbox 360 mods.
As one of my first electronc projects back in the day, I was quite pleased with the result.
As the buttons of the controller are made of a transparent material, you could make the inside hollow and glue some (colored) leds in them.
If you then connected the leds to the vibrator motor, the leds would turn on when the vibration motor turned on.
As finishing touch, a MW2 killstreak paintjob.