Conor Friedersdorf suggests an alternative to the diamond engagement ring. He proposes reselling the diamond and resetting the ring with a semi-precious stone, and then using the proceeds to fund a charitable donation. Then you have the signaling effects of the ring without tying up a bunch of wealth in a useless lump of carbon, while the fiancée gets the warm glow of feel-goodery from the donation.
One commenter points out the immediate depreciation of the diamond upon purchase, which can be easily solved by never buying the rock in the first place and just presenting your beloved with the cheaper ring and making the donation for the difference between retail ring prices. This makes it significantly more difficult to sparkle and shine your way into an affirmative proposal response, but surely your lady friend isn't so easily swayed by mere baubles. Well, let's hope so, anyway.
It was a good idea on Conor's part to sell this idea to the Hollywood crowd first. They seem an impressionable bunch. But from my (poorer, less sentimental) point of view this plan just shunts my semi-indignation from "Why am I supposed to spend two months salary on a lump of carbon just to prove my bona fides?" to "Why am I supposed give two months salary away to PETA just to prove my bona fides?" That's not much of an improvement.
I think a better idea yet would be to buy a ring, also sans diamond, and use the surplus money for a house down payment or the start of a college or retirement fund. The way I understand it the whole point of buying a diamond is to signal that you can afford to provide for a family. So why not use the money to start actually providing for a family? We just need some unique design that can act as a signaling device to the effect of "instead of having lots of wealth in an octahedrally crystallized bit of C-12 we are using said wealth to make a better life for our children." You can add your own subliminal "you do care about the children, don't you?" This, of course, is far too practical an idea to ever catch on as long as romance rears its head.
Of course this whole discussion is irrelevant. When the time is right I know I'll be marching off to a jewelry store for a rock regardless of how irrational it may seem now.