Manduca quinquemaculata. I noticed the damage yesterday on my Goose Creek tomato, and meant to find the bugger, but got distracted. Today it continued its rampage until I found it. Though very large (more than two inches long), these caterpillars are very hard to find, since they so closely resemble a tomato leaf. I find them by gently shaking the plant -- the hornworm "leaf" weighs so much more that it continues to bob after I stop shaking.
Given how quickly tomatoes grow, the damage they cause is pretty minor. I let the kids decide -- bucket of soapy water, or happy home next to the Swallowtail caterpillars. The kids gave me pollice verso and he's now contentedly munching on some tomato suckers I pulled for his delight.