So I must start out telling you that I have naturally curly, over-processed hair. I have tried a lot of different hair products and for any kind of heat, I use Silk Elements protection spray. It leaves my hair soft and silky feeling. I get it at Sally's Beauty Supply.
I also recommend using Coconut Milk by Organix for hair similar to mine. Not only does it help seal the hair... it smells awesome! I also mix in some Bed Head with it. Talk about awesome curl action!
When I flat iron my hair, I use wax to seal the ends. I never iron it completely straight. I always have a little flip at the ends. The wax helps keep it from frizzing out. Of course, Washington weather prevents me from doing this often. There is something about moisture in the air that my hair doesn't like.