Neck carry is my preferred method for a fixed blade. My favorite neck knife (and indeed, my favorite knife hands down) is my first Murray Carter necker. Here it is on the Continental Divide Trail:
I just haven't fully bonded with my second Carter necker. In all objective respects, it should be an "improvement" on my first, but it is just a little heavier and less comfortable to carry. I brought it on an Alaska bike tour this summer:
Honorable mention must go to my maple BRKT Mini Northstar. It's generally similar to my Carters, but stainless. Still seems like it has less absolute cutting power for similar dimensions and mass. Sorry no pics, it's in a few pieces today as I replace the hollow pins with mosaic.
I like the MNS so much I recently picked up another in maroon micarta/mosaic:
I also really like my Krein Ultimate Caper. I wanted one in 3V but the D2 is fine, the green fibermascus is beautiful and the grind is, of course, excellent. IMHO Krein kydex is excellent too. This is my lightest necker and the easiest to carry.
I've been tempted to get an Izula or Bravo Necker but I just don't like coated blades or skeleton handles. Although I know it is popular, I really dislike cord-wrapped neck knives. IME the paracord just absorbs sweat, oil, food, rain, etc.
jlamb, this thread has a ton of excellent suggestions. As you look for a "neck knife", I might suggest expanding your search beyond knives that are explicitly named such. Find any lightweight knife that appeals to you and have a neck sheath made.