A nice gift is a Kindle - If she reads much.
DO NOT get a cake with 50 candles on it.... Trust me on this!
When my mom turned 60 her friends got her a cake with the numeral candles on it. In front of everyone I said something was wrong with the cake. Then I turned the 6 upside down and said, there, all better.
Most of the guys here have hit it right. It's not so much about stuff, but more about spending time together doing what she likes or having someone do all the things that wives and moms do all the time ...the cleaning and household services is very good idea.
Flowers and cards and diamonds are tricky business. I know many women who like that stuff, and I don't get it. I would be upset if I got those things. I really don't get it.
The important thing to remember when gifting to a woman is the gift has to be personally significant (which is why so many hate appliances) so if it's a flowers, make it her favorite ones. Gift cards are dangerous business. They show lack of thought. I'd rather have to take something back to a store for an exchange simply because it means more to me that someone made the effort to pick something JUST FOR ME than not even make the attempt and cop out with a GC. With the exception of the music store where I have to get many of my supplies, or my coffeehouse, I hate getting GCs. I hate shopping, and those who really know me that a GC is not a good idea because I have to to shop to use it. It's like saying "I love you so much I'm going to make you do something you hate" TBH, I usually sell GCs and take the cash. Perfume? Usually make sure it is her scent to be safe unless she likes trying new ones already. And whatever you do, don't get a wife the same fragrance your mother wears! If you are buying clothes, this is dangerous. If not sure of size, err on the side of the smaller one. It will typically flatter her that you underestimated her size.
I tell you so much of that not so much so that you can know me, but to explain that it be personal and not a cliche gift idea, or if you do go with a standard, put a personal twist on it. Favorite color, fragrance, author, something like that. Maybe something sentimental, if she's the sentimental type, like some meaningful snapshots in a nice album according to her tastes
If she's a reader, look at the authors she already reads. Pick up a title she doesn't have and bundle it with some related literary items. Stuff you'd want or need when reading. booklight, mugs, favorite coffee or tea...but no toilet paper!