Cabbage worms are an easy one. Any product containing Bacillus Thurengiensis var. Berliner or Kurstaki will kill cabbage worms or almost any other caterpillar, but is non-toxic to all other organisms. B.T is a bacterium that attacks the digestive tract of caterpillars. Dipel Dust is the preferred product, but Thuricide liquid and other liquid brands are available and effective.
There are other varients of B.T. which control mosquito larva (var. Israelinsis, the active bacteria in Mosquito Dunks),
potato beetles, elm leaf beetles and other pests.
Here's a good article from Cornell University:
http://pmep.cce.cornell.edu/profiles/extoxnet/24d-captan/bt-ext.html
