OEM M3 springs will lower a stock 325e or 325i about 1.5-2". The spring rate is higher and is the same spring rate used for the 325is. The ride is stiffer, but not enough to sacrifice ride quality. The match up pretty well with Bisltein Sports.
If you aren't looking to lower the car and want some good, high qulaity springs, pick up some H&R OE Sport springs. At most they'll lower you about 0.5", but that's really nothing to worry about. For some good shocks, I'd consider Bilstein sports, Tokico Illuminas (adjustable) and Koni single adjustables - rangining from cheapest to most expensive. Konis are my preference.