Neck Knives: I really dig the CRKT Minimalist series after trying 30+ neck knives during my life, from Shcrade to S&W, other CRKT, ESEE, Becker and Ka-Bar, etc.
These are the best IMO. Small, unobtrusive, come with a razor sharp edge that's really really easy to sharpen and tune up. Soft steel, but enough for most folks.
They go completely unnoitced, sheath has great retention.
They can be worn in the belt as well (there's a specific attachment method), or go in the pocket.
They come in four different shapes, to suit your needs/particular tasks. Their handles are ergonomically perfect for me, comfortable and nicely designed.
I've only found one real contender, the Spyderco ARK. Released this past year, it is even lighter than any of the CRKT, thinner and its main selling point is its steel (H1) which can not rust.
It's designed to be worn 24/7, and no problem with that. You don't really notice it is there. You can swim at the sea, sleep with it, shower with it, and don't worry about it at all.
Its sheath offers great retention with minimal weight and imprint, it's so flat.
Tha main con of all these neck knives is edge retention, which is relatively low in both steels (3Cr13MoV and H1) but I find it enough for an entire day of tasks and EDCing jobs. YMMV