anyone know a good trustworthy site to order an aftermarket intake system for a 01-05 civic SI

No. And that's because an aftermarket intake is an aftermarket intake. They'll all do the same thing with roughly the same gains. You can go and spend $330 on AEM, Injen, HKS, Iceman or whatever you want. But you can get the same effects by making your own pipe and throwing a K&N (Which are proven in performance) for a fraction of that cost, and put that money elsewhere. Trust me when I say Spending over $150 on a name brand intake is a waste of money.

Most of em are trustworthy. depends on what brand your getting + for what need and the climate you mostly encounter. box intakes like the ARC are great cause you get air flowing from evrywhere so there are no restrictions and can also locate a hose near the lip for more cold air intake. pods come in two types, short arm and long arm. short arm your limited to the air within the bay but the long arm is more for cold air. but heres the catch with the long arm, raining days are gonna be a real problem to drive around in. when making a choice think what you want the part to do for you, whats your driving style, what other mods are going to be affected by the changes. Hope this helps.