I limit my personal spending weekly, that's how I (usually) stay out of the red. I usually spend 150-200 a week, not including groceries. A third of that 150-200 are essentials (toothpaste, cat litter, potting soil, any random stuff we need from Target that we ran out of). Other third is dining out. Usually spend $50 a week on going out for dinner/lunch. Final third goes towards things I want, like games, new movies, movie tickets, ebay buys, etc. Usually I spend $25-50 a week on unnecessary stuff.
Last week, for example, I spent $55 on Famitsu, HOTD Overkill and a Dreamcast game. This week I'm hitting a video game convention, limiting myself to $60. Week after that is Virtua Tennis 4, so I plan on not getting anything else.