How do you say very creative in French?

Depends what he or she creates! Somebody always making up new devices may be PLEIN D'IDEES, INGENIEUX, and that last Word really evokes technology. If he / she's into art or crafts, then we say TRES ARTISTE, but TRES CREATIF -IVE is also widely used. In fact, I do wonder what my HARRAP would suggest, but then they're 10 yards away... Hope this will help