I've had such a fab response from MN recently (other thread) that I am now ready to reveal a secret I said I never would!!
OLIVE OIL!!
Works brilliantly on my highlighted wavy/curly hair. You hardly need any (20p piece size if that). Avoid doing your roots but I find it defines my curls in a really natural non crispy way and also because I've chosen a light coloured oil it adds a nice sheen to the blonde bits (and possibly even brings them out a bit more).
Much better than Frizz Ease (where I would need almost a whole bottle every time!!), cheaper and more natural.
My hair is thick and reasonably coarse so dont know what would happen for people with fine hair..??
Good luck (and dont choose an olive oil with garlic etc in it!!)