It starts in your head. Just as you don't consider going to work as optional, don't consider biking to work as optional. Its just how you go to work.....period.

As other's have said routine and preperation the night before are key. For me, everything from exactly where my clothes are laid out, and where my bike lights are placed, to the precise spot in the refrigerator that I put my breakfast sandwich, is the same every day. That way, as I go through the first thirty minutes of each morning - from shower to out the door - on autopilot, I still somehow end up on my bike prepared and finally awake with the first pedal revolutions.