I have long, fine, straight hair that gets really tangled. Frederik Fekkai Coiff Defense gets all the knots out, and it's not even a detangler, it's technically a pre-style thermal/UV protectant. But seriously, it works so well.
But if you want something that's actually a detangler, I second the person above me. Kids detanglers all the best - L'Oreal's smells like pears! And it works!