A previous poster mentioned my 3 favorite neck knives (Emerson La Griffe, HAK, & Spyderco SPOT). The SPOTs are discontinued & while I've had an HAK, I'm not sure if they've worked through their problems (Someone else will have to give their opinion on that as I got mine when there weren't issues...yet).
I tend to like my neck knives with finger holes because it's easier to access (This is just for me). Neck knives tend to dangle & move around, so I've found that finger holes just make it easier to draw for me.
I also agree that lightweight & slimness is ideal as it makes it more comfortable to carry, especially after a long, hot day. If you don't mind a more traditional like grasp of the knife, that opens your options up quite a bit. The Hellion Nemesis comes to mind (Although I use that for my keychain knife) & Buck/Hartsook are the 1st 2 that come to mind, although there're definitely lots more.
If you're willing to carry a heavier knife, then the B/M's not bad (I've had one of those). I also like Newt Livesay's knives & if you don't mind the bulk, the Becker BK11 (Becker/Necker) has a great blade.
Hope that helps, although I'm sure others will come up with better choices.
Good luck.