The Defenders of Wildlife have a great, informative part of their web site, called "Saving Biodiversity: A Status Report on State Laws, Policies and Programs". I found it while browsing the web today. If you scroll down the page (I've linked to Massachusetts as an example), you will see that for each state, under the heading "Exotic Species," are the laws that state has to regulate non-native plants and animals. The column on the left allows you to go to any state's page. A valuable resource that is worth checking out.