I've been commuting 4-5 days a week since August. Having the right gear really helps, because I leave the house at 5:30am and the fear of being cold strikes icicles of fear into my little heart. Knowing I'll be roasty toasty (well, within reason) during the ride really helps.
Typically, the thought of how crabby and out of sorts I'll be if I skip riding is what makes me want to ride. On days I drive, I feel so HOT and gross (in the worst possible way). Also, as I ride, watching the sky gradually get hints of light in the east as I pedal along the river, well, there's nothing like it.