I would suggest you do a search on this site. You will find several very good threads on necks knives and a lot of reviews.
You also may want to consider getting a neck sheath for a knife you already have. I picked one up for my BM AFCK and really like it. The price was right as well since, I already owned the knife and kydex sheaths are generally pretty cheap. All in all, that option is working well for me.
Stay Sharp,
Sid