Our car looks like crap, too. My kids are old enough that I don't really have an excuse, but for those with busy toddlers, here's Sara's tip:
Although I feel like I do a decent job keeping the house in order, since Miss J. has joined us the car is usually a disaster area. I discovered that I can take advantage of J's love of 'driving' to do a leisurely job of scooping the trash and stuff out of the car. Sit her in the front seat, open all the doors, and she gets to drive to her heart's content while I clean.