Liquid Nymph

Liquid Nymph are makers of "handcrafted fetish jewellery" which primarily is a whole bunch of awesome collars, including french-maid themed ones, harem ones and some more traditional leather ones.  Expect a lot of lace and frills, and if you like that kind of thing you should go along and check them out.

blackxrossesxangel

Okay a little diversion from collars, there is an interesting Fetlife user called blackxrossesxangel who makes BDSM associated jewellery that I thought was quite cool.  The selection includes items featuring triskelions, slavebells, padlocks etc. ObCollarReference: May be good for adding dangly things to collars if you wish to spice them up :)

10 Sterling

10 Sterling are mostly a jewellery outfit as far as I can tell, however they do a range of "Neck Chains & Cords" that work quite well for subtle collars I think.  Many of these are reasonably high-end stuff, made from silver and titanium, but some of the more basic lines also feature neat tricks like magnetic links to hold them shut.  They also stock more collar-like things including stainless steel segmented collars and steel neck chains. If you're looking for more masculine subtle day collars many of this selection could totally work

Absolute Devotion

Absolute Devotion over at Etsy do a number of interesting collars, mostly in fabric and leather.  What drew my attention to them however was their line of brocade collars, with a fantastic mix of quite subtle ones, fantasticly shaped ones, wonderfully contoured ones and even ornate maid posture collars.  Really nice work, very inspiring :)

Spanking Good

Spanking Good do a whole line of basic but also functional and robust looking leather items.  Cuffs, collars, harnesses (of all kinds, including thigh-and-over-the-neck, a new one on me). The whole 9 yards, at very reasonable prices (in UK pounds no less).  They also apparently are happy to do whatever custom colour schemes and sizes you want.

Interestingly the site also has ankle cuffs designed to keep high heels on, something I've seen occasionally but not usually from the UK.

Cartier Love Collection

This is more just a general link: The Fabulous Duo (at Blogspot) reviewing the Cartier Love Collection, high end jewellery including rings, bracelets and necklaces that is screw-locking and designed to represent the bond of love.

Sir PollyPuma

Okay this is just a fantastic bit of work, a simple leather collar that is closed with poppers at one end, and in the middle of it are riveted two bits of leather forming the shape of a bow tie around the wearers neck.  Just so whimsical and cool :)

Bowtie Collar