Separate bank accounts
I read Scott Hanselmans post about allowance for adults. Me and my wife have separate bank accounts and one shared account. It affords us more freedom.
What Scott said really resonated with me, because me and my wife do the same kind of thing, only a little different. Scott and his wife have a shared bank account in which both their paychecks are being deposited and they get an allowance in a "private" bank account. From that private account, they can buy whatever they want.
Me and my wife reversed that idea, we each have our own bank account and deposit an (almost) equally amount in a shared bank account. Where I deposit 100 euro, my wife deposits 70 euro, but she does more household stuff to compensate. This is "easier" for her, as she works 3.5 days in a week. That 1.5 day is mostly spent cleaning and washing and occasionally lounging on the couch. This has a benefit that we don't have to do household chores during the weekend, which gives us more time for us.
From the shared account we pay everything that concerns us: groceries, mortgage, a date night, etc. We both have access to this account and check it regularly. We also discuss our financial "private" accounts with each other so we know how much we could spend on say a next house.
Now I said, I deposit 100 euros and my wife deposits 70, but that's not how much we make. Whatever is left is for us. We can do whatever we want with it. This way it is easier for us to surprise each other with a gift. I sometimes bring flowers and I like to know I buy them with the money I earned for the woman I love. Besides that, it's also easier to plan bigger surprises. When I proposed to her, we were already living together for 4 years. So it would be weird to explain why I spent sooo much money at a jeweller and it would ruin the surprise.
Besides those advantages, I also play with a bit of my money on the stock exchange. Now I have booked some small profit with that, but I have also lost a bit of that money on a hunch that didn't pay off. I wouldn't want to do such things with somebody else's money. In the end, I'll probably use the money for relationship activities such as dating or saving for a deposit on a new house. (Disclaimer, my profit is more in the range of a few nights out than the entire deposit on a house, but all bits count.)
Me and my wife still have separate bank accounts for our money, with which we do what we want. From there we deposit money in our shared account, which is used for relationship expenses. We have never fought over money and find it a very good system for us.