Cleaning up the kitchen after dinner if she's too tired or not feeling well.
Fixing things(or arranging them to get fixed) around the house
Dates - even going out to for a hamburger or ice cream for an hour or so is nice.
Buying little items she likes at the store without her asking (favorite cocoas, coffee, coffee creamers, fruit, cheese, snacks, candy bars, a book or video she's been wanting, etc)
When we have guests, Bill will often make the main dish so that all I have to do is pick up the house a bit and throw a quick dessert together.
Sometimes I'll be emptying the dishwasher and Bill will help me while we have a little conversation about our day.
If a child or other family member is calling, "MOOOOOOOOOOOOOOM or whatever" and you're home and it's something you can take care of, tell them Mom is busy and take care of the problem.
Tell your wife to invite some lady friends over for coffee and snacks and serve them the coffee and the snacks while they visit.
Carry in the groceries or other storebought goods for her and help her put them away.
Don't just tell her she's the most beautiful woman in the world, but the only woman in the world.