Yes, I couldn't find one and I looked, believe me! But neither does it say explictly that a wand is not needed. So personally I reckon it's still open. I tend to the view that wands aren't required, but I've found it difficult to write plots that depend on it because I never know which assumption readers are going to make.
(Hmm. It just struck me that a wandless aspect to Apparition could account for its difficulty.)

I suppose we'll find out in Book 7 if not before, as Harry will be old enough to learn by then.