I use a serum by redken called Smooth Down Heat Glide. I apply this to damp hair, mainly focusing on the ends.
Next after my hair is completely dry, before heat styling I apply Matrix Sleek.Look Iron Smoother, again focusing more on the ends.
I flatiron my hair almost daily and this helps alot.
After I am finished heat styling, I use Matrix Color.Smart Reflective Shine Spray allover my hair.
I cannot tell you how many people say "Oh wow your hair is SO shiny!" And it shocks them because I flatiron EVERYday and my hair is super dry and curly.
Those products are sort of pricy, but I only use them the days I wash my hair(following that whole regimen) and they last a REALLY long time.
I hope that helps; sorry it was so long.