Bt corn is now available in a great many products and with efficacy against a variety of insects. Also, a range of resistance management plans is associated with different hybrid families, some requiring an external refuge and some with the refuge seed already mixed into the bag at the appropriate rate.
As you choose hybrids, be sure that your selections have the insect control and herbicide tolerance traits you desire.
Entomologists at Michigan State University and the University of Wisconsin-Madison have developed a convenient publication summarizing all available Bt corn hybrids, their traits and refuge requirements. The Handy Bt Trait Table is available online.