IMHO now:
Neck knives should be:
1. lightweight
2. about 3" max blade length
3. secure grip, some kind of index finger "guard"
4. secure sheath
5. something stainless (or at least D2 or higher)
Stuff that fits my preference of what makes a good neck knife, sorta in order of my preference, but they are all nice IMO:
Darrel Ralph custom Arclite in CPM420V. The production version from Camillus in 420HC or whatever is a great buy, but I don't own one so can't comment on sheath.
http://www.darrelralph.com/ddr/straight/arc8w.jpg.html
RJ Martin's Handiman (would prefer ATS34 or 440C to D2 but that wouldn't stop me). I don't own one of these but have handled and would own one at right price.
http://www.robertsoncustomcutlery.com/rmarneck.htm
Bud Nealy mini Pesh Kabz
http://www.arizonacustomknives.com/nealy-bud.htm
Crawford's skeletonized version in ATS-34.
http://www.crawfordknives.com/html/NeckKnife.html
Kit Carson's F4 but in 420V. I like the large one better actually:
http://www.robertsoncustomcutlery.com/kitneck.htm
Mike Yurco makes a couple nice ones in 440C, but I don't have a pic of mine. Yurco is kind of unknown, don't think he has a web site... he was at Guild Shows and got one there.
Emerson LaGriffe is certainly very small and light. Kind of a wicked little claw as a last ditch, but not much of a utility knife. QA/QC is less an issue on EKI's fixed blades it appears:
http://www.emersonknives.com/Tact_index.html
There are other good ones....those above kinda illustrate what I like to see in a design.
I've never understood how people willingly carry anything over ~7" OAL or out of thick stock (especially unskeletonized) around their necks (I'm 5'-11") or out of carbon steel (e.g. Livesay) in the warm months. Sweat is full of salt. Need I say more.
For $20-$30 range, the Camillus ArcLite is best overall package I've seen so far.