Yup, they are tobacco hornworms (closely related to tomato hornworms but they eat both). Good thing you found them, and keep an eye out for any more because they can completely de-foliate a tomato plant in a couple of days. Voracious!
Picking them off by hand is the most effective method. We get them at the school garden each year, and the kids think it is the most fun thing ever to pick those big guys off the plants and let them crawl around on their gloves.
They metamorphose into a really neat looking huge, night-flying moth.
