I've been removing parts from my car that don't pull their own weight, or don't justify the amount of fuel required to push them through the airstream.
Removing the rear wiper was an easy decision. I seldom used the wiper, because RainX offers great visibility in the summer, and snow blows off of the rear glass if you can keep it above 20mph in the winter.
The mod is easy. Remove the wiper arm, the rear hatch trim, and the wiper motor, then replace the rear hatch trim if you think it pulls its weight (I don't). Go to the Misc. Hardware drawer of your hardware store and buy a 28mm / 1+3/32" plug, spray paint it black, and install it with clear silicone. The result is water-tight, aerodynamic, light-weight, and clean looking.
Removing the passenger mirror was a harder decision. The aero impact of a mirror is actually quite large, but you still need to be able to see what's in the blind spot to your right. Some people are happy relocating a mirror to inside the car, but I chose a camera and monitor. Back-up cameras are readily available, and I got the Pyle PLCM35 camera and monitor for around $75. It has a nice, wide field of view that completely eliminates the passenger side blind spot. It works great 22 hours of the day, but it's actually quite poor when bright sunlight shines on or near the monitor. Overall, I like it, but I recommend you choose a different (brighter) monitor.
I have a black coroplast enclosure keeping the mirror out of the rain at the moment, and I'm working on a fiberglass housing.
I've also blocked the upper radiator grille and half of the lower grille with fiberglass. My license plate can be mounted over the open portion of the lower grille in the winter, leaving the lower grille 20% open, or over the closed portion in the summer, leaving it 50% open.
Other items on the chopping block are the rear washer fluid nozzle, hoses, and pump (it's not very helpful to dribble washer fluid down your rear windshield, is it?), antenna (to be relocated to a more aerodynamic location, like the windshield), and maybe the driver's side mirror if I feel I can come up with a satisfactory replacement.
