I've always been a Schneider man. Paid full price for 10 of them a few years ago when I was just starting out (VERY dumb move). Today,
I have to say that Cavision's solid ND line is a tremendous value at $40 per filter. Honestly I don't notice that much of a difference compared to the more expensive brands. And in some ways I prefer the Cavision.
One of the turning points for me was that I dropped a 4x4 Schneider ND Grad and discovered that a replacement would be $212 + shipping. Screw that nonsense.
I will second the Cokin Z-pro series. The P-series isn't good for the HVX but the Z-pro series is a great value.
I bought a 0.6x for my HVX but usually I think that a tele would have been a better buy. The HVX is so wide already, there are very few places I can use a WA, and I could always rent it.