I like the work of Roger Schank, who has used constructivism in the development of goal-based scenarios and other models, and has been able to make them valuable to business leaders. That may be his most important contribution. Finally, I am interested in the whole arena of organizational learning, which I believe is often misunderstood. I don't necessarily believe that organizational learning is about training at all. To me, its about culture, leadership, networks and the behaviors that result when knowledge is shared.
Much more work is needed here.
Know the business you're in, and I don't mean just the instructional design business. Develop a very flexible model for yourself on how training is developed. Don't rely too much on specific models that may bog you down in the weeds of instructional design. Get involved in the profession. Professional development is essential and involvement outside your company will help you keep an open mind about your craft.