Check out the Apple refurbished store. You have to keep your eyes open, because good deals tend to get bought up quick, and there's no build to order option (though some people have reported getting unexpected, free RAM or harddrive upgrades).
Otherwise, the Apple Store is the way to go. Simple, fast, and effective. I hear Staples is clearing out remaining inventory right now, too, so get it while the getting is good, if there's any getting left.