I am wanting to preorder Episode I but was wondering where the best online store to do this? I found place called Playcentric and it has it for $19.90 including shipping. Has anyone heard of these guys and are they worthy? Are there any other stores with good prices? thanks for your help

Unless you are nowhere near a retail store, the general thinking is to wait to pick it up there because this will very like be a loss leader that can be had for less than current preorder pricing.
I would expect around $15.00
If you insist on preordering, Geoff posted a link here a while back that had it for under $20, and helped support DVDtalk.