There is no need to get anything other than OEM mirrors......but it seems like some people just want to waste money. Look at the pictures of the posts above with their new pricy mirrors.......I guess the guy just wants to see the side of his car and not cover ALL of the blind spot......
For the driver side mirror, roll up the window and press your head against the glass. Adjust the mirror so that you can just see the edge of the car. For the passenger side mirror, place your head in the center of the car (directly behind the inside mirror mount) and adjust the outside mirror so that you can just see the edge of the car. This is necessary even with convex (curved) mirrors where the image is distorted a little. - See more at:
How To Adjust Your Side-View Mirrors