A child, but since this is Friday Fluff, I will provide a material option.
BMW has a program called European Delivery. You buy and pick up your BMW in Munich, drive it around Europe for as long as you like, and then BMW will ship it back to the States for you when you're done. My ILs did it recently and had a blast. Please note that we can afford neither a BMW NOR a European vacation, so this is a total fantasy gift. When my wife and I had the "What would we do if we won the PowerBall Jackpot" conversation, this was near the top of her list.
If we had just a little more disposable cash, I would buy her a flat screen TV. Our current TV dates back to the early 2000s but works well enough that we haven't been able to justify a new one, and I know she hates it. She's currently saving up Amazon.com gift cards for it, but I'd like to buy it for her outright.
In Real Life, I did buy her a pretty nice watch, which I think she will love.