kahnos,
I would recommend checking out
fordpartsgiant.com. I've bought a multitude of Ford parts from them before and they offer the exact same OEM parts that your local dealer offers but at a nice discount. If you wish to stick with genuine OEM parts then I'd highly recommend them.
On a side note, I've had a few bad experiences ordering parts through Rockauto.com so I tend to avoid doing business with them from now on..