I'm partial to the Z fog lamp.
DIY: Rear Fog-Lamp "Z" light
New map light lenses - the GT-R lenses are popular.
Swap out the Nissan hamburger badges. There are a variety of popular options. I spray painted my EVO-R Z emblems to color match the car. I picked up spray from automotivetouchup.com with the Nissan paint code.
Spats if you don't already have them.
If you're still looking for performance mods, get a tune. Ecutek is highly rated, but Uprev will get the job done as well.
RJM clutch pedal if you have MT.
Aero bits. Lip and diffuser are good starts. Or go further and do bumper(s) or a full kit.