besides replacing the spark plugs, what else is recommended for this car?
100000 miles - requirements on 2001 BMW 325xi
BMW uses an inspection I and II system, so you should follow those recommendations. Any additions depend on the service history of your vehicle and its condition, so you need the advice of a good technician who inspects the car. You can use the Scheduled Maintenance estimates and additional services on RepairPal as a guide: http://repairpal.com/estimator