Ive seen alot of cam shaft sensors being replaced in E46's. They will cause a check engine light and I believe cost aroudn 50$. Not counting the 90$ dealer charge for install. The rims are pretty weak (what bmw rim isnt) so watch the pot holes. Window regulators are always being replaced.
Some other things Ive seen replaced:
water pumps/ thermostats
final stages aka blower resistors (control the a/c fan speed)
Theres alota 3 series in for check engine lights too.