WheelSto, Tire Rack, IND, GTMotoring, plus others shown in sponsor section:
I bought my wheels from wheelsto and was happy with their pricing and service.
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'04 E46 M3 - Jet Black - BBS E88, KW Clubsports, Brembo BBK, SuperSprint Exhaust