Well, I surprised her. My mother had passed me my grandmother's engagement ring, and although the diamond needed to be replaced (my grandfather was a poor GI returning from WWII--the diamond was .10 carat), the setting was absolutely gorgeous. It was white gold and gold, worked in a vine design and honestly was like nothing you'd find in stores today.
My fiancee had made it clear to me before that she wanted something simple, just a platinum or white gold band and a nice diamond, but I gambled. Between the sentimental value and the fact that the ring is honestly gorgeous, I figured I would do alright.
When I proposed, after the initial shock from her (I surprised her by proposing a lot earlier than she expected, so it was the last thing on her mind at the time), she looked like she was being nice when she said she liked the ring. I was scared out of my mind that she hated it, and was already plotting to tell her that we could easily put the diamond in a band more to her liking.
Thankfully, after wearing it for a few days and letting it sink in, it began to grow on her a LOT. Despite my repeated offers to take it to a store and buy her whatever band she wanted, she started to love it, and now would never trade it for another one. She just had to let it sink in a little and get over the fact that it wasn't exactly what she'd had in mind.