I like this bumper alot. Gemballa North America used to sell them on ebay but, I'm not finding any of their auctions now. I think they were around $700 on ebay.
http://uplode.us/up/gemballarear.jpg

Another alternative REAR bumper/diffuser
 

I found this one recently. Its very new, and it looks like it just covers up the bottom half of your rear bumper, like a lip. Not sure of the cost. Here is the pic and web site. This one is ONE PIECE, looks like a nice blend of the regular bumper and diffuser combined. You can thank me later. :D
http://i5.photobucket.com/albums/y15...er-02-rear.jpg

http://www.visracing.com/catalog/product_info.php?products_id=4285

I like the look of the grey bumper without the bumperettes. I saw someone refer to it as a euro-bumper. I would love to do that but have not seen one anywhere so I thought I would try the diffusers.

Anyone know of a source for no fiberglass? What modifications would you have to do for a '03 to fit, or would it?

I like the kokeln one.
http://www.kokeln.com/images/undertray.jpg

I would have bought it if my bypass valves werent there. It will work as a real diffuser, not just cosmetic.