This might sound crazy but my RLG ***PADDED*** armrest is one of my favorite mods. I added some foam when I installed it, about 1/2". It's quite nice compared to the hard plastic. I highly recommend anyone installing an armrest cover to get some padding too.
For the interior I also recommend a set of padded Focus headrests (wonderful, wonderful difference) and a rear shelf sticker bling mod (inspires every time you approach the car from behind).