Hi,
just registered but been a regular reader since I bought my 2006 X5 3.0 about 2 months ago.
This forum is amazing and I thought I might as well contribute.
Being from Europe, the "flat" side mirrors were driving me crazy, so I ordered some from Ebay.
They were a pain to install (it was difficult to remove the original ones, and had to slightly cut the edges of the slots of the new ones for them to go in), but the end result is great.
Here is a picture showing both mirrors for comparison. The aspherical is the installed one.
They were rather cheap ($25.85 for both left and right side mirrors), from Hong Kong, but as mentioned it was hell to get them in. Comparing with the original, the slots looked just minimally smaller, so it maybe just a problem of tolerances. The other potential issue is that the original ones have these "bands" in the back that I imagine to be the heating elements. On the ones I bought they are not visible, so not sure if these mirrors will heat. As I'm in Southern Florida, I'm not counting on this being a problem...