If you're having trouble controlling yourself as far as spending goes, I heard about the "ice glass" method in order to control your spending: put your credit card in a glass of water and then put it into the freezer. Next time your feel compelled to run out and buy a stack of clothes or shoes or electronics or whatever, there's a forced "cooling off" period, during which time you have to let the ice melt naturally before you can spend the money. (The microwave can't be used because it would corrupt the magnetic strip, and smashing the glass results in a mess.) By the time the card is thawed out, in theory, your impulse to buy whatever you wanted originally should be gone.

Personally, if there's something that I spend too much money on, it's books. By far, the biggest expense I have that isn't essential (my car, rent, or utilities fall into that category) is the amount I'm spending on books on Amazon. I probably spend well over $100 per month on books in general. I read almost all of them, though, so I don't think it's compulsive spending, and I don't hoard them, so I'm not convinced that it's really a problem. (My girlfriend might disagree.)

But my credit card number is stored with Amazon. Even if I froze my card, I could just as easily run to a computer and place a massive order for books without having to wait for the ice to melt. But what if Amazon allowed you to opt-in to a program where they "digitally freeze" your card on file, so that you had to wait an hour or so between the time you click "Checkout" from the shopping cart page and the time you could actually place the order? Or let customers set a "spending limit" each month. I could set mine at $80, and once I spend more than that, my card is frozen for all subsequent purchases. You could even create a page where you see an animation of the card, in an ice chunk, slowly dripping as it thawed out.

It would make you think before you bought anything, even before you hit the spending limit. It creates an artificial scarcity in the money you can spend, so you start evaluating whether each purchase you're about to make is "worth it". It might not increase Amazon's sales, but would demonstrate a commitment to putting a small segment of customers and their needs first.