alignment, wheel balence, bad ball joints, warped rotor (would be significantly worse when you applied breaks)
First, check the lugs, make sure they are all on there and torqued to around 80 ft/lbs, then try to wiggle the shit out of the wheel and see if it is loose in any way, if it is, then something is broken and that is bad. Get that wheel in the air and wiggle it again, if something is loose then get the suspension checked out. (try not to turn the wheel [ie: like you turned the steering wheel] very far since it could let the car shift if you are using a standard bmw jack) [PUT ON THE E-BRAKE & CHOCK WHEELS.]
You may have thrown a wheel weight, so get the tires balenced. If you can get them load balenced for not much more than a regular balence, thats better but not by much.
You can check the rotors yourself. Pump the brakes a bit to seat the brake pads. Then get the wheel in the air, quickly spin it by hand, and note how it slows down to a stop. If it slowly pulses to a stop, (even a tiny pulse!) then you have a warp in the rotor, if it just gradually slows down with no apparenty 'sticky' spots, it should be ok.
It's easier to notice the pulse if you take the wheel off and spin the rotor itself, less rotating mass which makes pulses more pronounced.
I would say you need new ball joints, so go ahead and get 2 new control arms with the ball joints pressed in, and new 96+ M3 LCA bushings.