* Tes cheveux sont magnifiques ! (This is a very common and straightforward way to say it. "Magnifique" means magnificent/gorgeous)
* Tes cheveux sont superbes ! ("Superbe" is another word for superb/gorgeous)
* Tes cheveux sont splendides ! ("Splendide" also translates to splendid/gorgeous)
* Tu as de magnifiques cheveux ! (You have magnificent hair!)
* Qu'est-ce que tu as de beaux cheveux ! (What beautiful hair you have!) This is a more emphatic way of saying it.
* J'adore tes cheveux ! (I love your hair!)
If you want to emphasize the healthy look of the hair, you could say:
* Tes cheveux sont en pleine santé ! (Your hair is very healthy!) While it doesn't directly mean "gorgeous," healthy hair is often considered gorgeous.
The best option to use will depend on context and who you are speaking with. The first two are the most common and suitable in most situations.