Yeah, just listen to what people have in their rides, and listen to how much the front is more important than the back. Usually stock speakers should be okay in the back for a while, after all, for the driver & passenger (how many of you really have 5 people in your car all the time? That's what I thought...) they don't hear much from the rear, and since bass is unidirectional, (or non-directional - it comes from everywhere) then you need a good sub setup and a good front stage, and the rear is just for fill.
If you can afford them, get kick panels in your car, the imaging is far superior compared to door speakers, unless you do some nice custom work with mid-bass drivers in the door & custom mount your tweets. And also, when searching for kick panels to mount the components, make sure you don't skimp on them - you get what you paid for. And one last thing - make sure the kicks (or doors) have sound dampening material in them, and the same deal with the trunk. Sound dampening may sound expensive and too much work, and not worth it, but the bass response, volume, and clarity that you achieve is well worth the expense.