I have to admit I'm pretty happy with my EMGOs.
They look very close to the stock ones, except for the weld on instead of bolt on mounting bracket and can be used for 38 or 40 mm headpipes.
They sound fine, and they go for less than a hundred bucks per side.
Just Google Images for EMGO BMW Muffler, but like I said, they look like the stock ones.
They also sell megaphones, peashooters etc.