I have a flowchart for purchasing new things. Liberally stolen from other people's ideas. It goes a little something like this:
1. Is this item necessary?
Yes = research the best one, then buy;
No = go to question 2.
2. Will this item bring me satisfaction or joy?
Strong Yes = buy;
Medium Yes = put on a list and revisit in 30 days. Buy if still desired;
Weak Yes = it's probably crap, resist the temporary urge;
No = why am I still standing in front of this thing?
It's a pretty simple litmus test that takes about 5-10 seconds of thought. Though, you do have to calibrate the difference between a strong and medium yes response. For me, a strong yes should happen once or twice a year.
Once you reach a happy level of stuff-ness, you can institute a one-in, one-out system when dealing with medium and weak yes's.