I bought my wife (fiancee at the time) a diamond engagement ring. Before MMM of course (at least I paid cash, didn't buy it on credit). I did the whole "diamond education" thing that so many men go through, reading a book or two about how diamonds are rated, getting quotes and reports on different rocks from various vendors, etc. The ring even came with a loupe so we could really see just how nice it is.
I knew my wife wouldn't care how much I spent or even if it was a real diamond. I knew that implicitly from knowing her so well, and she said as much after I gave it to her. Yet there was this unspoken sense of peer pressure when I bought it. All my friends were getting their wives (fairly big) rocks. She's never asked how much it cost; I know she doesn't care.
That said, it is beautiful. When it's cleaned and polished (which is never, now that we have kids), and sunlight hits it, it sparkles wonderfully. Granted, the pleasure we get out of seeing that isn't proportional to what it cost! Still, I don't regret buying it. It is extremely valuable to us, not in terms of money, but in terms of being symbolic of our marriage, and the accompanying sentimental value. If it were lost, the money wouldn't bother me nearly as much as the fact that it's "the one" I gave to her. In other words, I'd value it just as dearly if it were a cheapie I picked up a the dollar store.
She loves the ring, but what she loves more is the fact that I picked it out all by myself and totally surprised her with it. And I have zero fashion sense, so the fact that I really stepped out of my comfort zone for this meant a lot to her. The funny thing was, I had no idea what size ring she wore; so I just guessed, and was off so much that it actually fit my finger! She didn't want to send away to have it re-sized at first because she wanted to wear it. So for the first week or so, she had to use this clear plastic "tubing" on part of the ring to pad it up enough that it stayed on her finger.