hand picking works great from smaller gardens..I remember my grandfather would pay us 50 cents per worm...that was ages ago som now it might be more like a buck.
the above link has some more tips.
I planted Marigolds all the way round my tomatoes last year. They worked well until the very end of the growing season. I only found 2 worms the entire season and they were on my potato plants...however Idid not plant Marigolds around my potatoes, but I will this year.
If you want to use a chemical, try liquid sevin
Or if you want to hand pick use tweezers if you are squimish about touching them
If you want to try something natural there is something called Thuricide. It must be mixed fresh and will only harm caterpillars - nothing else.