Tobacco hornworm (Manduca sexta).

tj

Remove that Tomato/Tobacco Hornworn, they will hang on quite tightly with those feet in the rear, and feed them to the birds. Cut the bugger in half. If there are more and much smaller then spraying with Bacillus thiringiensis - Kurstaki can help keep them under control.
There is a wee wasp, Braconid, that might parasitize these so if you see any hornwarms that have what look like rice hulls on their backs leave those alone.

Personally I don't like to kill the hornworms because I enjoy seeing the large sphinx moths that come from them. Near the woods and edge of the cornfield by my property is an area where Jimsonweed reseeds every year. I have taken hornworms from my tomato plants and released them on the jimsonweed, and they manage to feed on that and complete their life cycle (I think). But the last few years the parasitoid wasps are always beating me to the caterpillars and killing them before they get over about 2-2.5" long.

There are some 100 different Sphinx moths, including the Hummingbird Moth, that some people mistakingly think come from the Tomato/Tobbaco Hornworm. The adults moths of the Tomato/Tobbaco Hornworm, the Carolina Sphinx and the Five Spotted Hawkmoth, are rather bland, not too exciting, moths. The larva of these feed on plants of the nightshade family, which the Jimsonweed is a member, so if you have some growing around you that might be an option. However, if you don't it will not be.

Yuck! I just found one of these today on my tomato plant & didn't know what it was. Husband smooshed it!