It's been covered a number of times in these forums -- might be an idea to sticky one of the threads to the top.
A quick look at the ConceptArt.Org Atelier's site would get you a look at their concept art courses:
Orthographic Concept and Production Design
Industrial Design, Vehicle, Technology, Prop and Item Creation
Animal Anatomy and Creature Design
Drawing and painting from your imagination are a given. Knowing how things need to be rigged and animated certainly helps and many job offers ask for 3D experience.