I'd also look into the BMW Performance Springs (yellow ones). They are pretty close to the M3 rates, IIRC.
Right now, Bilsteins are the only shocks/struts available. Konis should be available soon.
There is a thread where a 328i driver used M3 front springs, linear rear springs, and custom valved Bilsteins to mimic the M3 setup. He seemed pretty pleased.