Golf tee( kinda useless but its free and cool)
Remove cowl to hear more engine noise.
Unplug the diverter valves and plug holes its a diy blow off valve sound.
Good mods for the money:
Dci about $100 makes a nice sound and increases air flow.
Tune- $700+ best part about the n54 is tuning it! ( no dash lights, clears codes and its proven to be as reliable as stock)
Downpipes- under 400 for vrsf, reduce backprrssure, more sound and power, morr turbo spool!