I wasn't able to read through the entire thread, so I'm not sure if it was mentioned...but a Jewish tradition (Still practiced mainly by the very conservative and orthodox subsets) is to not have a ring at all before the couple is actually married, and an engagement jewelry piece is chosen instead! This can be anything, really, as it is simply a token to represent the impending marriage! Most couples choose to have a necklace or bracelet, and these pieces can cost as much or more than a ring! (Just to add to the background; After the wedding, most couples DO get a sparkly/meaningful ring to go with their plain wedding bands if the bride wants one. For some couples, the engagement token is something relatively cheap and most of the money goes towards a ring, but for others a ring is never bought and the token is worn very prominently every day!)
I'm much more religious/traditional than my family members are, and most of my friends etc. follow this tradition as I also intend to do- without fail, every time I've told my mother or nonJewish/nonobservant friends that XYZfriend got such a beautiful necklace/watch/bracelet/whatever for their engagement I always get a very snarky response! It doesn't matter that the couple is very happy with their choice, or that it is their tradition, or that the token can be more expensive/impressive than the ring they THINK the couple should have...the point is that it isn't a diamond ring on her finger, and for some reason that means that the couple isn't actually engaged or the groom to be is a cheapo! But of course, after the wedding when the ring is on the new bride's finger, clearly the groom had some sort of light bulb go off that he shouldn't be an awful person. (Of course, this after the tradition is explained for the 3294328459348323011 time.
Somehow, I imagine I'll be having a very tough time with my family when the time comes for ME to be engaged!