If you want to put a lip, you'll have to change your rear bumper since yours has the diffuser (I assume that -> no pics in your gallery). Any rear bumper from a FoFo sedan will fit. If you want to change it, F2 makes a nice kit for the '05+ model (http://www.f2focus.com).
Well damnit I didn't know they made the RS kit for the 05's, it's about time. I guess it's time to save up a grand for parts, then money for labor and paint after I get back from vacation. Oh yeah, and shipping too, can't forget the shipping.