Recently I started keeping a wishlist of things I wanted to buy, however, not just now. It also helps with having a 'cooling down' period after I decide I want-want-want something, as advised by many personal finance blogs out there (in one form or the other). At first I thought it was silly, I'd remember the things, but after using it for a while I found it actually really helps.
Not only does this immediately stop me from impulse buying, it also helps me (eventually) buy more focussed. When I put an item on the list, I also put the price I found it for next to it, and where I saw it. Usually, I'll also add a photo to it. (I use Shopper on my iPhone, which I also use for my normal groceries).
By adding the price, I can keep my eye open for a special offer for the same product, or, when I decide I really want to buy it, I can do focussed research to find the product at the best price.
I did do research before, especially for needed items, but my wants sort of slipped past that research stage more quickly. By keeping this list I force myself to not only wait, I also make sure I do plenty of research (and then in the process drop the product all together).
I've also noticed it becomes easier to throw things of the list after a while, and this in turn leads to it getting easier to not want to put something on there to begin with. Don't want to waste my time with things I won't buy anyway :)
By seeing the silly stuff on my list, I feel less tempted by more silly stuff. And seeing the total amount doesn't hurt either!
I currently have 5 items on my list (I dropped some earlier):
1. Griffin Clarifi iPhone case
2. Neocube magnets
3. Sigg Thermo Mug
4. Portable foldable water-drinking reservoir for the dog
5. A 5x5x5 Rubik's Cube
All wants, I don't need any of them really. They're just so much fun! ;)