I've found wishlists are a good way of curbing my impulse buying habits - any time I see something new that I like, there's that immediate impulse that it's the greatest thing ever and I need to buy it now. Putting it on a wishlist is a weird mental trick for my brain that I have 'collected' it and kind of already possess it, without actually buying it. 99% of the time when I come back to it a few weeks later, that impulse has evaporated and don't buy it. (My amazon wishlist has over 1,000 books on it now!)
My Steam list isn't that bad - only 77 games on it at the moment and a lot of these are old games I already own and just want to have on Steam for convenience.